Le charbon demeure à l’heure actuelle l’un des combustibles fossiles les plus couramment employés afin de produire de l’énergie. Son utilisation accrue dans le futur devra toutefois être conciliée avec la problématique de réduction des émissions de gaz à effet de serre. Des procédés permettant de limiter les émissions de CO2 ou de faciliter son captage, à l’image de l’oxycombustion, sont de fait actuellement développés. Leur implémentation à l’échelle industrielle implique toutefois de lever un certain nombre de verrous scientifiques liés à la compréhension des mécanismes physico-chimiques d’oxydation du charbon pulvérisé sous atmosphères plus ou moins riches en oxygène. Ce travail de thèse a de fait porté sur la mise au point d’un banc d’essais de laboratoire permettant d’étudier la combustion du charbon en reproduisant des conditions de chauffe analogues à celles rencontrées industriellement. Le brûleur hybride qui a été mis au point lors de ce travail a permis d’analyser des flammes jets de combustible solide sous atmosphères O2/N2 et O2/CO2 contenant des teneurs variables en oxygène. Une caractérisation détaillée des champs de vitesse et de température dans la chambre réactionnelle a été opérée. Des mesures de température des semi-cokes dans les flammes et de concentrations d’espèces gazeuses (CO, CO2, O2, NO, NOx et SOx) ont également été réalisées tout au long de la combustion. Des prélèvements de semi-cokes à différents temps de séjour ont enfin été opérés de sorte à obtenir des profils de dévolatilisation qui ont pu être confrontés à divers modèles empiriques issus de la littérature. L’ensemble des données que nous avons obtenues nous a permis de mettre en évidence l’impact d’un enrichissement en oxygène du milieu réactionnel sur les cinétiques de dévolatilisation et sur les mécanismes de formation de polluants tels que les NOx et les SOx. Les travaux menés sous oxycombustion ont pour leur part permis de mieux appréhender les différences fondamentales entre la combustion du charbon pulvérisé sous air et sous atmosphères O2/CO2. Pour terminer, des essais préliminaires de combustion de mélanges à base de charbon et de bois ont également été menés, la co-combustion de charbon et de biomasse constituant un autre moyen de limiter les quantités nettes de CO2 émises dans l’atmosphère. / Coal is currently one of the most widely used fossil-fuel for energy production applications. Its increasing use in the near future will have to face the greenhouse gas reduction objectives. Different processes have thus been developed to reduce CO2 emissions or ease their capture as oxy-fuel combustion for instance. The implementation of such techniques at industrial scale implies fundamental works to be undertaken to better understand the physical-chemical processes involved in the oxidation of pulverized coal under oxygen enriched environments. The present work has thus focused on the development of a lab-scale test bench allowing the study of coal combustion with heating rates similar to those met in industrial combustors. The hybrid burner that has been set up allowed the analysis of different solid fuels jet-flames under O2/N2 and O2/CO2 atmospheres containing various amounts of oxygen. A detailed characterization of the velocity and temperature fields has been carried out in the combustion chamber. Char temperatures and gaseous species concentrations (CO, CO2, O2, NO, NOx and SOx) have also been monitored during the combustion. Char samples at different residence times have finally been collected to derive devolatilization profiles that have been compared to simulated data issued from various empirical models from the literature. Obtained results clearly illustrate the impact of an oxygen enrichment of the reaction medium on devolatilization kinetics and pollutants formation including NOx and SOx. Works conducted in the fields of oxy-fuel combustion allowed to better understand the fundamental differences between pulverized coal combustion under air and O2/CO2 environment. Finally, preliminary experiments have been conducted using coal and wood blends since coal co-combustion with biomass appears to be another interesting mean to reduce net CO2 emissions into the atmosphere.

In this work the combustion characteristics of coal, charcoal, microalgae biomass and blends between these three components were evaluated by means of non-isothermal thermogravimetry. Blends between coal, charcoal and microalgae biomass were made according to the specifications of a D-optimal mixture design so as to be able to model interactions between the three components with maximum precision despite multiple constraints built into the design. These constraints specified that coal can have a minimum value of 70 mass percent in any blend, while microalgae can have a maximum value of 20 mass percent. While coal and charcoal were blended by mixing the two respective dry components, microalgae biomass was incorporated into the blends by first absorbing microalgae onto fine coal from concentrated slurry of the microalgae in water. The microalgae in these blends were therefore intimately associated with the coal. This approach differed substantially from the normal practice of preparing coal – biomass blends (which are usually dry-mixed as for coal – charcoal blends). Proximate analyses of the starting materials showed that the microalgae biomass has a significantly higher volatile matter: fixed carbon content than both coal and charcoal, which should improve the combustion of these materials by providing a more stable combustion flame. Analyses of the thermogravimetric data obtained showed that coal and charcoal have much simpler combustion profiles than microalgae biomass for which five different thermal events could be observed in the DTG combustion profile. Qualitative kinetic analyses showed that the combustion of coal and charcoal follows first-order kinetics, but for microalgae biomass combustion, the first two combustion stages appear to follow first-order kinetics. The TG and DTG profiles for coal, charcoal, microalgae and blends of these three components were used to derive values for the so-called comprehensive combustion property index (S-value), which provides a combined measure of the ease of ignition, rate of combustion, and burn-out temperature. The S-values so obtained were used as response variable for the construction of a response surface model in the experimental domain investigated. Following statistical validation of the response surface model, the model was used to predict an optimum S-value or a blend that would display optimum combustion behaviour. Two optimum blends were obtained from the optimisation process, one in which only charcoal is added to coal, and one in which only microalgae is added to coal. Adding both charcoal and microalgae produced an antagonistic effect compared to when only one of these are used. Qualitative kinetic analyses of the combustion data of blends indicate that blends of coal and charcoal combust in a manner similar to the individual components (hence following first-order kinetics), but blends of coal and microalgae follow more complex kinetics despite the fact that the combustion profile is visibly more simple compared to the combustion profile for microalgae alone.

Today the use of resources in the industry are not complete to be considered as sustainable from the perspective of nutrient recovery. In the Swedish pulp and paper industry residual streams such as bark, fiber reject and sludge are returned for more sustainable use more frequently. Around 300 000-600 000 tons of sludge is generated every year from different cleaning processes in the pulp and paper industry. About 15 % of that sludge is so called biosludge that is a result from biological water treatment, where large amounts of phosphorus are used. After the cleaning process the total amount of biosludge generated in Sweden each year is estimated to contain approximately 2000 tons of phosphorus (P). The most common way to discard the biosludge today is by incineration, where aspects such as high content of moisture and ash have proven to be problematic. Besides phosphorus, other elements such as sulfur (S), chlorine (Cl) and calcium (Ca) are often found in the biosludge in larger amounts.   This study included co-combustion experiments of current residual streams from the pulp and paper mill SCA Obbola AB where the aim was to investigate how the ash transformation chemistry was affected. The residual streams comprised of bark, fiber reject and biosludge which were combusted together with stem wood in a bench scaled bubbling fluidized bed. To investigate if different ash related operating and technical problems could be reduced and if there was potential of phosphorus recycling from the ashes, produced ash and other samples were examined by SEM/EDS. The fuel mix from SCA Obbola consisted of large amounts of Ca, S and P relative to more ordinary biomass fuels like stem wood. These elements originated from the biosludge and was confirmed by the fuel analysis. Analysis made on collected samples showed that Ca and P together formed phosphates that either stayed in the bed or was collected in the cyclone which indicated that there could be a potential for recovering phosphorus. Although, the Ca/P ratio in the ashes was too high, which probably leads to that phosphates unsuitable for nutrient recovery are formed.   The fiber reject from SCA Obbola contained large amounts of chlorine according to the fuel analysis which was indicated from the results later in the study. During the combustion most of the Cl left the bottom ash via volatilization. It was true for both the fuel blends with and without fiber reject. When larger amounts of biosludge was added to the fuel mix less of the corrosive compound potassium chloride (KCl) was found in depositions and collected fine particulate matter (PM). This was due to that more sulfur was added in the system when the amount of biosludge was increased which lead to that K reacted with SO2 instead of Cl and formed K2SO4. The observed reduction of KCl resulted in; 1) lower amounts of fine particulate matter which means less loaded particulate filters 2) less risk of high temperature corrosion on heat transfer surfaces. The general conclusion that could be drawn from this study was that by increasing the amount of biosludge in the fuel blend at already high mixings of fiber reject, problems such as corrosion and fine particulate matter could be reduced. These advantages must be considered to the amount of lime stone needed to be added for reducing HCl from a cost perspective.

Increasing environmental legislations on pollutant emissions originated from fossil fuel combustion and intention of increasing the life of existing fossil fuels give rise to the use of renewable sources. Biomass at this juncture, with its renewable nature and lower pollutant emission levels becomes an attractive energy resource. However, only seasonal availability of biomass and operation problems caused by high alkaline content of biomass ash restrict its combustion alone. These problems can be overcome by co-combustion of biomass with lignite. With its high fuel flexibility and high combustion efficiency, fluidized bed combustion is the most promising technology for co-firing. To improve and optimize the operation of co-firing systems a detailed understanding of co-combustion of coal and biomass is necessary, which can be achieved both with experiments and modeling studies. For this purpose, a comprehensive system model of fluidized bed combustor, previously developed and tested for prediction of combustion behaviour of fluidized bed combustors fired with lignite was extended to co-firing lignite with biomass by incorporating volatile release, char combustion and population balance for biomass. The model predictions were validated against experimental measurements taken on METU 0.3 MWt AFBC fired with lignite only, lignite with limestone addition and about 50/50 lignite/olive residue mixture with limestone addition. Predicted and measured temperatures and concentrations of gaseous species along the combustor were found to be in good agreement. Introduction of biomass to lignite was found to decrease SO2 emissions but did not affect NO emissions significantly.

Effective use of resources is essential in the development towards a sustainable industry. Waste products, such as sludge from industrial waste water treatment, often contain valuable reserves of plant nutrients but this resource is nonetheless commonly disposed of as contaminated waste.  Approximately 1 500 ton phosphorus per year is added in biological waste water treatment at the Swedish pulp and paper industries and this non-renewable resource thereby ends up in their so called biosludge. The most common way to discard the sludge is by incineration. Besides the high levels of phosphorus, the biosludge usually contains high levels of moisture and ash forming elements, sulfur and chlorine, which makes it a rather problematic fuel. The aim with this study was to investigate different aspects on ash transformation chemistry during co-combustion of biosludge, from the pulp and paper mill SCA Packaging Obbola AB, with wood fuels and wheat straw. The phosphorus recovery potential, and the effects on deposit formation and emissions,  were examined by SEM-EDS- and XRD-analysis of ash from co-combustion experiments. The experimental results were complemented with theoretical analysis based on thermochemical equilibrium calculations. The biosludge from SCA Obbola contained high levels of Ca which had a large impact on the ash transformation reactions. Most of the phosphorus from the fuels stayed in the solid ash during combustion, and in all ash assortments, except for the pure wood fuel, it was primarily found in the crystalline structure whitlockite, Ca9(K,Mg,Fe)(PO4)7. Hydroxyapatite, Ca5(PO4)3OH, was identified in ash from combustion of the pure wood fuel and wheat straw, and in the mixture of biosludge and wood fuels with the lowest proportion of sludge. Of the two phosphorus compounds, hydroxyapatite is more difficult to break down. It is therefore promising from a phosphorus recovery perspective that whitlockite was the main phosphorus compound in most of the ash assortments. Some of the sulfur in the sludge reacted with Ca and formed solid CaSO4, which stayed in solid ash during combustion, while chlorine generally left the bottom ash by volatilization. K- and Si-rich agricultural residues, such as wheat straw, are associated with a number of ash-related problems, including deposit formation due to low ash-melting points. During co-combustion of biosludge and wheat straw, the melting tendencies of the wheat straw ash elements were examined. According to the thermochemical equilibrium calculations, the composition of the mixed fuels would result in a significantly higher initial slag formation temperature compared to the pure wheat straw. This trend was also observed in the experimental results. It is likely that the relatively high levels of Ca, Al and P in the sludge all contributed to reduced slag formation in the wheat straw ash, by formation of ash compounds with higher melting temperatures. The high calcium levels may however have reduced some of the positive effects of increased P and Al contents by these elements preferably reacting with Ca instead of capturing alkali in crystalline structures.

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

In the efforts to create sustainable production of heat and power and to reduce the net CO2 emissions to the atmosphere, alternative fuels are today being utilised. These fuels are, for example, biofuels and waste derived fuels such as different residues from the agricultural sector and the pulp and paper industry, municipal sewage sludge and municipal sorted solid waste. These fuels put new demands on the combustion facilities due to their chemical composition and this in turn calls for methods of prediction for the evaluation of their combustion behaviour. Most significant for the majority of these fuels are the high alkali and chlorine concentrations which cause bed agglomeration, deposit formation and corrosion on heat transfer surfaces. These problems can be solved if sufficient knowledge is obtained of the specific fuel or fuel mix. In this work, chemical fractionation, a step by step leaching method, was used on fuels, fuel mixes and fly ashes from co-combustion in a fluidised bed combustor. In addition, XRD and SEM-EDX were used for the fuel and fly ash characterisation. Different alkali chloride reducing additives i.e. kaolin, zeolites and sulphur were investigated as was the influence of various bed materials: silica sand, olivine sand and blast furnace slag (BFS). Some of the new, alternative fuels, such as municipal sewage sludge and meat and bone meal (MBM) contain high concentrations of phosphorus which is a very important nutrient essential in many biological processes. Phosphorus rock used as raw material in the phosphate industry is a depleting natural resource estimated to last for only 30-200 years according to different sources. The combustion of municipal sewage sludge enriches the phosphorus in the ashes while hazardous components such as pathogens and organic pollutants are rendered harmless after combustion. However, toxic heavy metals are also enriched in the ashes. One aim of the work was to find a sufficiently effective and low cost method for phosphorus extraction from fly ashes derived from municipal sewage sludge combustion. Two types of municipal sewage sludges were investigated using different chemicals for the phosphorus cleaning step in the waste water treatment plants. The first sewage sludge derived from a plant using iron sulphate as flocculant to precipitate phosphorus as iron phosphate. The second sludge meanwhile came from a plant using aluminium sulphate as flocculant to precipitate phosphorus as aluminium phosphate. Both sewage sludges were dewatered prior to combustion and co-combusted with wood pellets. At pH 1 nearly all the phosphorus was released from the fly ash derived from the sewage sludge where aluminium sulphate was used as a phosphorus precipitation agent. Iron sulphate as precipitant inhibited the phosphorus extraction from the ashes, resulting in only 50-80% of the phosphorus being released. Furthermore, the mobility of heavy metals to the leachates was investigated to establish whether the leachates were suitable as fertilisers. Only minor fractions of Pd, Hg, Cr, Cu, Mn, Co, Ni, As, Sb, V and Zn were found in the leachates, all well within the legislated limitations for fertilisers. However, one exception was Cd that was nearly totally dissolved in the leachate. Thus a decadmiation of the leachate is necessary prior to any utilisation of the ashes and reuse of phosphorus as fertiliser. / <p>Akademisk avhandling för avläggande av teknologie doktorsexamen vid Chalmers tekniska högskola försvaras vid offentlig disputation den 15 oktober 2008</p>

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Agradecemos a compreensão. on 2017-03-22T14:39:39Z (GMT) / Submitted by NATALIA DA SILVA RIBEIRO null (nsribeiro2@gmail.com) on 2017-03-22T17:58:52Z No. of bitstreams: 1 Defesa Natalia_Final..pdf: 3778151 bytes, checksum: 08fb9f490ae966bed7312cca924c9c9e (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-03-23T16:23:04Z (GMT) No. of bitstreams: 1 ribeiro_ns_me_guara.pdf: 3778151 bytes, checksum: 08fb9f490ae966bed7312cca924c9c9e (MD5) / Made available in DSpace on 2017-03-23T16:23:04Z (GMT). No. of bitstreams: 1 ribeiro_ns_me_guara.pdf: 3778151 bytes, checksum: 08fb9f490ae966bed7312cca924c9c9e (MD5) Previous issue date: 2017-03-03 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Nesta dissertação, investiga-se através da análise termogravimétrica o comportamento da combustão de amostras de carvão mineral, bagaço de cana-de-açúcar, bagaço de sorgo biomassa e das misturas de carvão-biomassa. A biomassa e o carvão possuem propriedades físico-químicas diferentes que proporcionam comportamento térmico diferente durante o processo de co-combustão, desta forma o objetivo desta pesquisa é caracterizar o comportamento térmico de misturas de carvão mineral com bagaço de cana-de-açúcar e bagaço de sorgo em atmosferas simuladas de combustão (O2/N2) e oxicombustão (O2/CO2). Os experimentos foram realizados em duplicata em um analisador termogravimétrico utilizando uma razão de aquecimento de 10 °C/min. Foi considerada uma granulometria uniforme para todos os materiais (63 µm) com a finalidade de garantir uma mistura homogênea. Foram estudadas quatro proporções de biomassa na mistura (10, 25, 50 e 75%). A partir das técnicas de termogravimetria (TG) e termogravimetria derivada (DTG) foram determinados parâmetros tais como Índice de combustão, sinergismo e energia de ativação, bem como avaliada a influência da atmosfera de combustão sobre esses parâmetros. Os resultados indicam que o bagaço de cana-de-açúcar apresenta valor de energia de ativação inferior ao registrado para o bagaço de sorgo e desempenho de combustão superior ao do bagaço de sorgo. Para as misturas, os melhores resultados foram registrados até a proporção de 25% de biomassa na mistura. Avaliando individualmente cada material, quando se substitui o N2 por CO2 pode-se observar um aumento na reatividade da reação, uma maior oxidação dos materiais e uma melhora nos parâmetros avaliados. Para ambas as misturas não foram observadas mudanças significativas no perfil de combustão quando o N2 é substituído por CO2. No entanto, a presença da biomassa na co-combustão com o carvão, além dos benefícios econômicos e ambientais, aumentou o desempenho da combustão do carvão mineral em ambas as atmosferas. / This dissertation investigates by thermogravimetric analysis the behavior of the combustion of coal, sugarcane bagasse, sorghum biomass bagasse and coal-biomass blends. The biomass and coal have different physicochemical properties that provide different thermal behavior during the process of co-combustion, thus the aim of this research is to characterize the thermal behavior of coal mixed with sugarcane bagasse and sorghum bagasse in simulated atmospheres of combustion (O2/N2) and oxycombustion (O2/CO2). The experiments were performed in duplicate in a thermogravimetric analyzer using a heating rate of 10 ° C/min. A uniform particle size for all materials (63 μm) in order to ensure a homogeneous mixture was considered. Four biomass ratios were studied in the blend (10, 25, 50 and 75%). From the techniques of Thermogravimetry (TG) and Derivative Thermogravimetry (DTG) curves were determined parameters such as: Combustion index, synergism and activation energy and evaluated the influence of combustion atmosphere on these parameters. The results indicate that the sugarcane bagasse presents a lower activation energy value than sorghum bagasse and combustion performance higher than sorghum bagasse. For mixtures, best results were recorded up to 25% proportion of biomass in the blend. Individually evaluating each material, when replacing N2 by CO2 can be seen an increase in the reactivity of the reaction, the increased oxidation of the materials and an improvement in the evaluated parameters. For both blends, no significant changes in combustion profile when N2 substituted by CO2. However, the presence of biomass in co-combustion with coal in addition to economic and environmental benefits increased the combustion performance of coal in both atmospheres. / CNPq: 134366/2015-8

The co-firing technology of coal with biomass has been implemented to enhance the usage of biomass in power generation, thus reducing the release of greenhouse gas emissions. This study deals with the fireside issues, namely ash-related issues that arise during co-combustion of coal and biomass takes place. Ash release from biomass can lead to ash deposition problems such as fouling and slagging on surfacesof power generation boilers. The scope of this work includes the development of a conceptual model that predicts the ash release behaviour and chemical composition of inorganics in coal and biomass when combusted. An advanced analytical method was developed and introduced in this work to determine the speciation of biomass.The method known as pH extraction analysis was used to determine the inorganic speciation in three biomass samples, namely wood chips, wood bark and straw. The speciation of biomass and coal was used as an input to the model to predict the behaviour and release of ash. It was found that the main gas phases during the combustion of biomass are KCl, NaCl, K2SO4 and Na2SO4. Gas-to-particle formation calculations were carried out to determine the chemical composition of coal andbiomass when cooling takes place in the boiler. The results obtained in this work can be used in future work to determine the ash deposition of coal and biomass in boilers.

This thesis deals with the design of a co-combustion gas boiler for coal gas and blast furnace gas mixture. The calculation includes stoichiometry, determinination of the boiler efficiency, steam production rate and heating surfaces sizing. This thesis also includes technical documentation of designed gas boiler. The calculation of the boiler meets the values specified by the scripts and also by documentation from PBS. The boiler was designed for 113.9 MW and 93.77 % efficiency.