Deflector effects in fixed bed (biomass) combustors and non-combusting packed beds

Combustion can be used to thermally process biomass fuels and yield both heat and power in a sustainable manner. At present, direct combustion of solid biomass is the primary approach for generating electricity and heat when these fuels are used at a commercial scale. Deflectors have been used in the freeboard section of industrial combustors to reduce radiant heat loss through flue gases and for particle emissions abatement. Freeboard deflectors can also influence emissions and freeboard temperature distributions by changing the flow dynamics. Despite much research into laboratory scale biomass combustion and packed beds, there have been no systematic studies into the impact of deflectors (heat shields) on the axial and radial temperature profiles, test methodologies used or the emissions in laboratory scale fixed bed biomass combustors operated on pelletised fuels. Through a combination of experiments and numerical simulations, this research has investigated such issues in both high temperature fixed bed biomass combustors as well as relatively lower temperature (non-combusting) packed beds subject to different heating modes. Experiments have been carried out on a laboratory scale (continuous feed) fixed bed combustor featuring both primary air (supplied through the fuel bed) as well as secondary air (in the freeboard). A freeboard deflector was located at different axial locations during this testing. The aim was to characterize deflector effects on burning rate, temperature distribution (near-wall and near-centreline) and gaseous emissions (NO, CO, CO2) over a range of primary and secondary air flow rates. A systematic method has been developed to establish the steady state time period during the combustion process. In this regard, detailed analyses on the time series of thermocouples, emissions and fuel mass conversion data have been performed. The proposed method is based on calculating the percentile mean deviation of temperature and NO/CO emissions data which can provide a more effective means of resolving the stand of the steady state operating, compared to only using the time evolution of these variables. In addition, the significance of the thermocouple radiative corrections (losses) and its effect on the accuracy of measured temperatures has been investigated. The results concluded that NO, CO and CO2 emissions are affected by the presence of a deflector in the mid-range of combustion stoichiometry (λ=0.439-0.509). However, deflector effects were found to be most prominent for NO and CO emissions by reducing and rising their levels, respectively. Deflectors affect upstream near-wall temperatures, but their impact depends on relative (axial) position (H). Furthermore, results reveal that deflectors do not have significant effects on the burning rate and flow availability of the exhaust gases. A CFD model of a porous media has been implanted to study the effects of freeboard deflectors on the heat transfer inside packed bed columns for the temperature range of 100°C to 400°C (which is typical for drying and volatile release in biomass combustion). Results show that the deflector do affect temperature profiles along the freeboard as well as wall temperatures but this is dependent on the mode of heating and emissivity of the deflector

Mitigation of large-scale organic waste damage incorporating a demonstration of a closed loop conversion of poultry waste to energy at the point of source (2000-LS-1-M2) Final Report

peer-reviewedThe increase in the world population and urbanisation, have changed the way the world produces food. As the demand for cheap and readily available food in the developed world increases, high-density, intensive farming practices have replaced subsistence farming to allow for the mass production of food. An unavoidable consequence of these farming\ud practices is the generation of significant quantities of organic waste

Integration of a model for volatile release in the CFD simulation of an industrial biomass boiler

Doctoral Thesis for PhD degree in Leaders for Technical IndustriesMotivada por sua disponibilidade, abundância generalizada e preocupações ambientais, a biomassa sólida tornou-se uma opção competitiva para diversificar a produção de eletricidade entre os recursos de energia renovável. Este trabalho tem como objetivo caraterizar o comportamento da combustão de espécies de biomassa frequentemente utilizadas em centrais termoelétricas para suportar o desenvolvimento de um modelo numérico para modelação eficiente e precisa da conversão de biomassa numa caldeira industrial a grelha. A eficiência da caldeira numa central de 35 MWth foi calculada como sendo aproximadamente 80%. Amostras selecionadas de biomassa de eucalipto, pinheiro, acácia e oliveira foram testadas com o analisador térmico Hot Disk TPS 2500S. A condutividade térmica ficou compreendida entre 0,239 e 0,404 W/mK. Além disso, a capacidade calorífica apresentou uma variação entre 0,855 e 2,442 MJ/m3K, e a difusividade térmica entre 0,187 e 0,258 mm2/s. Para a análise final e aproximada foram utilizados os equipamentos LECO TruSpec CHN Macro e LECO CS-200 e uma mufla, respetivamente. Os dados revelaram uma maior reatividade do eucalipto, cerca de 2 vezes superior aos outros combustíveis, e a propensão da acácia a produzir emissões poluentes (principalmente à base de azoto) e problemas de deposição de cinzas devido à sua composição química. Amostras de pequenas dimensões (cerca de 10 mg) foram usadas para medir a perda de massa e a sua reatividade num analisador termogravimétrico (TGA) da TA Instruments, modelo SDT 2960. Os testes foram realizados em atmosfera oxidante, a uma taxa de aquecimento entre 5 e 100 ºC/min, até 900 ºC. Observou-se que numa ampla faixa de temperaturas, a conversão do combustível segue uma sequência de secagem, desvolatilização e combustão do resíduo carbonoso. Amostras de maiores dimensões foram testadas num reator construído para esse fim, e que simula o processo de desvolatilização de forma controlável. Neste, a perda de massa foi medida continuamente ao longo do tempo enquanto os compostos da fase gasosa foram recolhidos em sacos para posterior análise num cromatógrafo gasoso da Bruker Scion 456-GC equipado com um detetor de condutividade térmica. Ao contrário dos dados do TGA, concluiu-se que na oxidação de biomassas, utilizando partículas maiores, não é possível distinguir as sucessivas etapas de conversão, devido à maior resistência interna de difusão. Avaliando a influência da esbelteza da amostra (rácio comprimento/espessura), concluiu-se que a taxa de desvolatilização depende apenas da sua espessura e não do volume. Além disso, para temperaturas mais altas do reator, a taxa de perda de massa é independente do tipo de biomassa. Os compostos gasosos libertados durante a conversão térmica do eucalipto apresentaram forte correlação com a temperatura do reator, sendo CO2 e CO sempre os principais produtos de desvolatilização. A dependência da temperatura de ambos os compostos apresentam, para o CO, um aumento de 8 a 13% entre 600 e 800°C, enquanto o de CO2 aumenta apenas ligeiramente de 11 a 12%. O modelo eXtended Discrete Element Method foi usado para descrever a desvolatilização no reator. Os resultados foram comparados com os dados experimentais e, embora tenha sido observada uma boa concordância, concluiu-se que a oxidação do resíduo carbonoso necessita de um modelo de difusão. A simulação do escoamento no interior da caldeira foi feita utilizando o software ANSYS Fluent. Neste, um modelo empírico externo para prever a conversão de biomassa ao longo da grelha é acoplado a um modelo CFD para prever o escoamento reativo dentro da caldeira. Os resultados destacaram a contribuição da contração na seção intermédia da fornalha, e a necessidade de um maior caudal de ar secundário para reduzir as emissões de CO. Os resultados mostram que modificando a razão entre o ar primário e secundário de 79/21 para 40/60, obteve-se uma redução da fração mássica de CO de 0.009 para 0.0003.Motivated by their availability, widespread abundance, and environmental concerns, solid biomass has become a competitive option to diversify electricity production amongst the renewable energy resources. This work aims to characterize the combustion behavior of solid biomass species frequently used in power plants as a route to support the development of a numerical model for efficient and accurate modeling of biomass conversion in an industrial grate-fired boiler. The boiler efficiency of a power plant rated at 35 MWth was calculated as approximately 80%. Selected samples of biomass (eucalyptus, pine, acacia, and olive) were tested with a Hot Disk Thermal Constants Analyzer TPS 2500S. The thermal conductivity, varied in the range of 0.239 to 0.404 W/mK. In addition, the heat capacity is within 0.855 to 2.442 MJ/m3K, and the thermal diffusivity is between 0.187 and 0.258 mm2/s. The ultimate and proximity analysis was carried out on the fuel samples using LECO TruSpec CHN Macro and LECO CS-200 equipment and a muffle furnace, respectively. The data revealed a higher reactivity of eucalyptus, which is around 2 times higher than that of other fuels, and the propensity of the acacia to produce pollutant emissions (mostly Nitrogen based) and ash deposition problems due to their chemical composition. Small size samples (around 10 mg each) were used to measure the mass loss and their reactivity in a thermogravimetric analyzer (TGA) from TA Instruments, model SDT 2960. The tests were carried out on an oxidizing atmosphere at a heating rate between 5 and 100 ºC/min up to 900 ºC. It was observed that over a wide range of temperatures, fuel conversion follows a sequence of drying, devolatilization, and char combustion. Larger samples of heartwood were tested in a purpose built reactor that simulates the devolatilization process under a controllable manner. In this, the mass loss was continuously measured along the time while the gas phase compounds were collected in bags for subsequent analysis in a gas chromatograph Bruker Scion 456-GC equipped with a thermal conductivity detector. As opposed to the TGA data, it was concluded that all fuels show that the combustion of large particles does not exhibit separate consecutive conversion stages, due to internal diffusion resistance. This was further highlighted by varying the sample aspect ratio. It was concluded that the devolatilization rate depends on the smallest dimension and not on the bulk size. Furthermore, at higher reactor temperatures, the mass loss profile is independent of the biomass. The gas compounds released with eucalyptus presented a strong correlation with the reactor temperature, being CO2 and CO always the main devolatilization products. The temperature dependence of both compounds shows, for CO, an increase from 8 to 13% between 600 and 800 °C, while the CO2 yield is only slightly increasing from 11 to 12%. The eXtended Discrete Element Method model was implemented to describe the devolatilization inside the reactor. The results were compared with the experimental data and, while a good agreement was observed, it was concluded that the char oxidation needs to be also represented by a diffusion model. The numerical model was developed using the ANSYS Fluent software. In this, a user defined empirical model to predict the biomass conversion along the grate was coupled with a freeboard model to predict reactive flow inside the boiler. The results highlighted the contribution of the converging sections in the middle section of the furnace and the need for a higher secondary air flow rate to reduce CO emissions. The results show that a reduction of the CO mass fraction from 0.009 to 0.0003 was possible with a modification of the primary to secondary air split ratio from 79/21 to 40/60.Fundação para a Ciência e a Tecnologia for sponsoring my research, through the grant SFRH/BD/130588/2017

Volumetric combustion of biomass for CO 2 and NOx reduction in coal-fired boilers

To meet the urgent environmental targets, substituting coal with biomass has been considered to be an effective and promising method over the last decades. In this paper, a new concept of volumetric combustion is proposed and further developed to achieve 100% fuel switching to biomass in large scale coal-fired boilers. Volumetric combustion not only changes the in-furnace flow but also affects the combustion reactions by the intensive mixing and internal recirculation of the flue gases. Firstly, the volumetric combustion properties of the wood pellets were investigated experimentally. An Aspen model was then used to thermodynamically describe and study the volumetric combustion with three different types of fuel, and the emission properties of CO 2 and NOx were compared. Finally, two applications of volumetric combustion were discussed. It is concluded that the wood pellets ignited and combusted much faster than the coal pellets and had a larger combustion volume when combusted under lower oxygen concentration conditions, and the ignition time was almost independent of the oxygen concentration when the oxidizer was preheated to 1000 °C. In addition, the NOx emissions decreased as the recirculation ratio of the flue gas increased, and as the percentage of biomass used in co-firing increased, the amount of flue gas that needs to be recycled for reduction of NOx decreased. Thus, the volumetric combustion is beneficial as it reduces the operation cost of NOx reduction. The volumetric combustion would be an attractive technology for co-firing a large proportion of biomass in coal-fired boilers with high boiler efficiency and effective emissions reduction

Combustion Performance of Agropellets in an Experimental Fixed Bed Reactor versus a Commercial Grate Boiler. Validation of Ash Behavior

Agrobiomass is presented as a suitable alternative to contribute to the fossil fuel decarbonization strategy at the European level. To achieve the ambitious objectives established in this regard: (i) new biomass resources need to be used and therefore initially tested in order to confirm its potential for different applications, such as energy production, and (ii) biomass supply capacity needs to be enlarged; therefore, agroindustries converted into Integrated Biomass Logistic Center (IBLC) can play a key role. In this research, eight different agropellets (blends of wheat straw and maize stalk with forestry wood) were produced in a IBLC and tested in a commercial boiler, comparing the results with previous ones obtained in a fixed bed reactor test campaign and to a base case (woody pellets). This paper includes both individual results in terms of bottom ash, deposition, and a final comparison of ash behavior in both facilities. All biofuels tested showed an adequate performance in terms of efficiency and emissions, being slightly better for the agropellets produced with wheat straw. Regarding sintering and deposition, the tendencies found in the reactor investigation were also observed in the commercial boiler. Moreover, the assessment of the results from the boiler and reactor’s tests proved that reactor experiments are representative and may be used to test new biofuels more efficiently in terms of effort and time allocated and could be used to predict sintering and deposition phenomenon occurrence

Biomass for Energy Country Specific Show Case Studies

In many domestic and industrial processes, vast percentages of primary energy are produced by the combustion of fossil fuels. Apart from diminishing the source of fossil fuels and the increasing risk of higher costs and energy security, the impact on the environment is worsening continually. Renewables are becoming very popular, but are, at present, more expensive than fossil fuels, especially photovoltaics and hydropower. Biomass is one of the most established and common sources of fuel known to mankind, and has been in continuous use for domestic heating and cooking over the years, especially in poorer communities. The use of biomass to produce electricity is interesting and is gaining ground. There are several ways to produce electricity from biomass. Steam and gas turbine technology is well established but requires temperatures in excess of 250 °C to work effectively. The organic Rankine cycle (ORC), where low-boiling-point organic solutions can be used to tailor the appropriate solution, is particularly successful for relatively low temperature heat sources, such as waste heat from coal, gas and biomass burners. Other relatively recent technologies have become more visible, such as the Stirling engine and thermo-electric generators are particularly useful for small power production. However, the uptake of renewables in general, and biomass in particular, is still considered somewhat risky due to the lack of best practice examples to demonstrate how efficient the technology is today. Hence, the call for this Special Issue, focusing on country files, so that different nations’ experiences can be shared and best practices can be published, is warranted. This is realistic, as it seems that some nations have different attitudes to biomass, perhaps due to resource availability, or the technology needed to utilize biomass. Therefore, I suggest that we go forward with this theme, and encourage scientists and engineers who are researching in this field to present case studies related to different countries. I certainly have one case study for the UK to present

Características químicas e toxicológicas de partículas de queima doméstica de biomassa

Biomass combustion for residential heating is recognised as an important source of particulate matter, not only in the ambient air, but also inside the dwellings. Exposure to biomass burning particles has been linked to a vast array of adverse health effects. The physical and chemical properties of inhaled particles are thought to greatly affect the biological responses. Over the years, many studies have focused on emission source profiles of residential biomass combustion. However, with the advent and growing market share of new small-scale appliances automatically fed with compressed biofuels, research efforts need to be devoted to the characterisation of emissions from these appliances either from new commercially available pellets or from pellets made from potentially relevant raw materials. Despite the wealth of publications on emissions and composition of particles from residential biomass combustion, the impact of this source on the indoor air quality has been scarcely studied, especially with regard to the chemical and toxicological characteristics of the particles. The two main objectives of this thesis were: i) to obtain chemical and toxicological profiles for pellet-fuelled heating systems, and ii) to evaluate the impact of traditional appliances on indoor air quality, properties of particulate matter, deposited dose in the respiratory tract and biological responses. For the fulfilment of the first objective, four types of pellets were selected (two brands of ENplus A1 certified pellets, one brand of non-certified pellets, and laboratory-produced acacia pellets) to carry out experiments in a laboratory combustion facility to determine emission factors of gaseous compounds and particulate matter (PM10). To achieve the second objective, particulate samples were collected in two households equipped with distinct combustion appliances (open fireplace and woodstove) in the absence of other indoor sources. The dose of inhaled indoor particles deposited in the human respiratory tract was estimated using an exposure dose model (ExDoM2). The chemical composition of PM10 from both laboratory experiments and residential microenvironments was analysed for water soluble inorganic ions, organic and elemental carbon and detailed organic speciation. Additionally, in samples collected indoors, major and trace elements were also determined. A battery of in vitro assays was used to assess the ecotoxicity, cytotoxicity and mutagenicity of the PM10 samples. The results obtained from the laboratory measurements indicated that the alternative woody raw material selected for pelletising contributed to a dramatic increase in particulate emissions, with distinctive chemical properties and increased toxicological potential. It was observed that even certified material does not always meet emission requirements set by the Ecodesign directive. Particles from pellet combustion were mainly composed of water soluble inorganic constituents. The carbonaceous fraction of particulate samples from commercial pellets was dominated by elemental carbon, while organic carbon was the most abundant constituent in samples from the combustion of acacia pellets. The results showed that particles from acacia pellets were the most ecotoxic and cytotoxic, while mutagenicity was not detected for any biofuel. In the sampling campaign carried out in residential microenvironments while using different combustion devices, higher exposures, higher doses in the human respiratory tract and higher toxicity of the particles collected during the operation of the open fireplace were observed, as a result of the lower combustion efficiency. When using this combustion equipment, a higher increase in particulate matter levels (over 12 times compared to background concentrations) was registered compared to that measured with the woodstove (2-fold increase). The carbonaceous material accounted for a PM10 mass fraction of about 44% in samples from the room equipped with fireplace, while the woodstove operation almost halved the total particulate carbon content. Water soluble ions and trace elements showed variable contributions to the mass of the indoor particles and were generally higher during the operation of the woodstove. Several chemical markers of biomass combustion were detected in both residential microenvironments, highlighting the input of this source to indoor particles. The bioreactivity assessment showed that particles emitted by the fireplace were the most ecotoxic and cytotoxic, while mutagenicity was not detected in any of the tested samples. Combustion-related organic compounds in indoor particles, such as polycyclic aromatic hydrocarbons, displayed significant correlations with the increase in toxicity. In view of the results obtained, homeowners should be encouraged to upgrade the wood burning technology in order to reduce the products of incomplete combustion inside their dwellings.A combustão de biomassa para aquecimento residencial é reconhecida como uma fonte importante de material particulado não apenas no ar ambiente, mas também no interior das habitações. A exposição a partículas resultantes da queima de biomassa tem sido associada a um vasto leque de efeitos adversos na saúde. Sabe-se que as propriedades físicas e químicas das partículas inaladas afetam acentuadamente as respostas biológicas. Ao longo dos anos, muitos estudos tiveram como foco os perfis de emissão da combustão residencial de biomassa. No entanto, com o aparecimento e a crescente quota de mercado de novos equipamentos de pequena escala alimentados automaticamente com biocombustíveis prensados, a investigação deve ser direcionada para a caracterização das emissões desses sistemas de combustão alimentados quer com novos pellets disponíveis no mercado, quer com pellets produzidos a partir de novas matérias primas potencialmente relevantes. Apesar da abundância de publicações dedicadas às emissões e composição das partículas da queima residencial de biomassa, o impacto desta fonte na qualidade do ar interior tem sido pouco estudado, sobretudo no que diz respeito às características químicas e toxicológicas do material particulado. Os dois objetivos principais desta tese foram: i) obter os perfis químicos e toxicológicos para sistemas alimentados a pellets, e ii) avaliar o impacto de equipamentos tradicionais na qualidade do ar interior, propriedades do material particulado, dose depositada no trato respiratório e respostas biológicas. Para atingir o primeiro objetivo, foram selecionados quatro tipos de pellets (duas marcas de pellets com certificação ENplus A1, uma marca de pellets sem certificação e pellets de acácia produzidos em laboratório) para realizar experiências numa instalação laboratorial de combustão e determinar fatores de emissão de gases e material particulado (PM10). Para atingir o segundo objetivo, realizaram-se amostragens de partículas em duas habitações com equipamentos de combustão distintos (lareira aberta e recuperador de calor), na ausência de outras fontes interiores. A dose de partículas inaladas no interior das habitações e depositadas no trato respiratório humano foi estimada utilizando um modelo de exposição/dose (ExDoM2). A composição química das PM10 resultantes quer dos ensaios laboratoriais, quer dos microambientes residenciais, foi analisada em termos de iões inorgânicos solúveis em água, carbono orgânico e elementar e especiação orgânica detalhada. Adicionalmente, nas amostras de partículas colhidas no interior das habitações, foram também determinados elementos maioritários e traço. Foi utilizada uma bateria de ensaios in vitro para avaliar a ecotoxicidade, citotoxicidade e mutagenicidade das amostras de PM10. Os resultados obtidos nos ensaios laboratoriais indicaram que o material lenhoso alternativo selecionado para a peletização contribuiu para um aumento dramático das emissões de partículas, as quais apresentaram propriedades químicas distintas e um potencial toxicológico elevado. Observou-se que mesmo o material certificado nem sempre cumpre os requisitos de emissão estabelecidos pela diretiva Ecodesign. As partículas emitidas pela combustão de pellets apresentaram na sua composição maioritariamente iões inorgânicos solúveis em água. O carbono elementar dominou a fração de material carbonáceo nas partículas dos pellets comerciais, ao passo que o carbono orgânico constitui a componente mais abundante nas amostras resultantes da queima de pellets de acácia. Os resultados mostraram que as partículas dos pellets de acácia foram as mais ecotóxicas e citotóxicas, enquanto não foi detetada mutagenicidade para nenhum biocombustível. Na campanha de amostragem realizada em microambientes residenciais durante a utilização de diferentes equipamentos de combustão, observou-se uma exposição mais elevada, dose depositada no trato respiratório humano mais alta e uma toxidade superior para as partículas colhidas durante a operação da lareira aberta, refletindo a menor eficiência de combustão deste equipamento. Durante a sua utilização, foi registado um aumento superior nos níveis de material particulado (mais de 12 vezes relativamente às concentrações de fundo) em comparação com o observado para o recuperador de calor (aumento de 2 vezes). O material carbonáceo representou cerca de 44% da massa de PM10 nas amostras colhidas durante a operação da lareira, enquanto a operação do recuperador de calor reduziu quase pela metade o conteúdo total de carbono nas partículas. Os iões solúveis em água e os elementos apresentaram contribuições variáveis para a massa das partículas no interior das habitações, sendo geralmente superiores durante a operação do recuperador de calor. Em ambos os microambientes residenciais foram detetados vários traçadores químicos de combustão de biomassa, assinalando a contribuição desta fonte para as partículas interiores. A avaliação da biorreatividade revelou que as partículas emitidas pela lareira foram as mais ecotóxicas e citotóxicas, enquanto que não foi detetada mutagenicidade em quaisquer das amostras testadas. Vários constituintes detetados nas partículas internas, como os hidrocarbonetos aromáticos policíclicos, apresentaram correlações significativas com o aumento da toxicidade. Considerando os resultados obtidos, os proprietários devem ser encorajados a atualizar a tecnologia de combustão, a fim de reduzir os produtos de combustão incompleta dentro das suas habitações.Programa Doutoral em Ciências e Engenharia do Ambient

Modelling ash deposition during air firing of high percentages of biomass with coal

This project is aimed towards an understanding of ash deposition during air firing of high percentages of biomass with coal. Biomass resources are widely used as sustainable, renewable and environmentally friendly materials. There has been an increase in the use of biomass for power generation by means of co-firing with coal as well as by the combustion of 100% biomass. Despite the advantages of biomass in reducing carbon emissions from the electricity sector, the co-firing of high percentages of biomass can potentially aggravate ash related problems in the boiler. In order to develop mitigation strategies for the formation of deposits, an understanding of the ash behaviour during the combustion of high percentages of biomass is required. To understand ash deposition, the influence of the inorganics, crystal types, and complex compound formation should not be neglected. In this work, ash samples from El Cerrejon coal and pine, wheat straw, white wood pellet biomass were characterised for their inorganic composition by X-ray fluorescence (XRF) and wet chemical methods. Relationships between these two methods were found and a modification to the standard test method has been recommended to improve the accuracy of the XRF method. Furthermore, the melting behaviour of ashes from pure El Cerrejon coal, biomasses, and their blends were studied through ash fusion tests and via a method using a simultaneous thermal analyser coupled to mass spectrometer (STA-MS) for the evolved gas analysis. The inorganic composition were used to calculate indices to determine the slagging and fouling potential of pure fuel ash, ash blends and ash produced by ashing blended fuels (fuel blends ash). Base-to-acid ratio (Rb/a) results indicate that pine ash has a higher slagging potential than coal ash, which is not consistent with the experimental ash fusion measurements. Viscosity models appear to perform better for high-coal content blends than high-biomass content fuel, and further refinement is required for modelling the viscosity of pure biomass ash as well as high co-firing percentages. Thermodynamic modelling of slag formation was undertaken using the FactSage model and verified by XRD analysis for the solid phase. XRD showed complex interactions between inorganics which changed with biomass type, blend ratio and temperature. The FactSage model was successful in predicting the changes of gas, solid and liquid phases during pure biomass, coal and co-combustion, and for most of the blends studied the prediction of slag formation was within 100°C of the measured experimental ash melting window

Impact of fuel quality and burner capacity on the performance of wood pellet stove

Pellet stoves may play an important role in Serbia in the future when fossil fuel fired conventional heating appliances are replaced by more efficient and environmentally friendly devices. Experimental investigation was conducted in order to examine the influence of wood pellet quality, as well as burner capacity (6, 8, and 10 kW), used in the same stove configuration, on the performance of pellet stove with declared nameplate capacity of 8 kW. The results obtained showed that in case of nominal load and combustion of pellets recommended by the stove manufacturer, stove efficiency of 80.03% was achieved The use of lower quality pellet caused additional 1.13 kW reduction in heat output in case of nominal load and 0.63 kW in case of reduced load This was attributed to less favourable properties and lower bulk and particle density of lower quality pellet. The use of different burner capacity has shown to have little effect on heat output and efficiency of the stove when pre-set values in the control system of the stove were not altered It is concluded that replacement of the burner only is not sufficient to increase/decrease the declared capacity of the same stove configuration, meaning that additional measures are necessaly. These measures include a new set-up of the stove control system, which needy to be properly adjusted for each alteration in stove configuration. Without the adjustment mentioned, declared capacity of the stove cannot be altered, while its CO emission shall be considerably increase