This study presents the results of an experimental investigation of wood combustion. Variables chosen for investigation were fuel feed rate, fuel moisture content, fuel particle size, excess air, fraction and temperature of under-fire air. Data recorded during the experiments included the composition and temperature of the combustion products in the combustion chamber, particulate emissions and combustible fraction of the particulate. Most mathematical models describing the combustion of wood particles require numerical solutions. For this investigation, an alternative model was used to generate closed form solutions for the determination of the burning times for wood particles in the combustion chamber. The model results were in good agreement with the experimental findings. The temperature profiles of combustion products within the combustion chamber were closely estimated, using an analytical model developed for this investigation. The composition profiles within the combustion chamber were estimated with the use of a chemical equilibrium model. These models were in good agreement with the experimental results for the estimation of the oxygen and carbon dioxide contents of the combustion products. The chemical equilibrium model proved to be inadequate for the determination of the NO[subscript x] and CO contents of the combustion products. Based upon the experimental data, a linear regression model was developed to investigate the variables affecting the combustion process. A computer model was used to calculate the temperature and composition of the combustion products under adiabatic conditions. Over the range of the variables considered, it was concluded that combustion efficiency and particulate emissions were most influenced by the factors that increased the volume and velocity of combustion products in the chamber. Moreover, it was also concluded that the part-load operation of the combustion unit resulted in higher particulate emissions and lower combustion efficiency. / Graduation date: 1991

Thesis (M.S.)--California Polytechnic State University, 2009. / Title from PDF title page; viewed on February 2, 2010. Major professor: Tracy Thatcher, Ph.D. "Presented to the faculty of California Polytechnic State University, San Luis Obispo." "In partial fulfillment of the requirements for the degree [of] Master of Science in Civil and Environmental Engineering." "June 2009." Includes bibliographical references (p. 70-78).

Packed bed combustors burn fairly large solid fuel particles within confining walls, with air supplied from below the grate. As combustion occurs and particles are consumed, fresh particles are fed onto the bed so the level is kept roughly constant. Packed bed combustion is used for wood and biomass combustion in small-scale power plants, wood waste combustion in pulp and paper plants, and trash incineration. The structure of a packed bed is very important to the combustion process and can be defined by particle shape and size, sphericity, particle overlap (decreasing area availability) and chiefly by void fraction. Void fraction has already been proven of great influence in packed beds – it is raised to the third power in the pressure loss equation, and it can also affect heat and mass transfer and surface reaction rates. This thesis presents results of several experimental combustion tests that were performed in a packed bed combustor, using commercial spruce lumber particles of parallelepipedal geometry as fuel. At the end of each test the bed contents were removed, taking care to preserve their structure, and fixed with liquefied wax. The solidified bed was then cut into circular cross sections at different heights of the bed, and photographs of the cross sections were taken so the local void fraction could be estimated using image analysis. The bed sampling led to the discovery that, surprisingly, the actual bulk void fraction in the combustor, which is the average of local void fraction measurements, is less than that of the unburnt particles, varying from 19% to 30% in decrease in void fraction depending on the particle type used. Local measurements allowed the development of an empirical linear equation model to represent the variation of void fraction with height above the grate. Each combustion test had measurements of gas volume fractions and temperatures at different heights above the bed grate to be compared with the results of a numerical model simulation. The numerical model used in this work is an existing numerical model of all the relevant processes in packed bed combustion. Previously, the numerical model had assumed the void fraction to be constant and equal to that of the unburnt fuel, since no information on local variation was available, and the packing geometry remained self-similar as particles are consumed. Three models for void fraction were then compared in the combustion model: a constant void equal to that of the unburnt particles, the empirical linear fit of void fraction with height, and a constant void equal to the measured bulk void fraction. Maximum temperatures were higher using the unburnt fuel void fraction because of a thicker oxidation zone, whereas the void fraction model iii based on experiments generated a thicker reduction zone and therefore higher CO concentrations. CO concentrations were experimentally measured and agreed quite well with the CO concentration from the model. Local void fraction differences had the most impact in the diffusion-controlled zone, as shown by comparing the empirical void model and the measured bulk void fraction. How lowering the void fraction can increase gas velocities, heat and mass transfer coefficients, and burning rates is also discussed in this work.

Climate change and its accompanying environmental issues have caused the building industry to use more environmentally friendly building materials. Wood have always been a buildingmaterial but due to the renewed interest in imparting sustainability and renewability, its usage has increased over the recent years. With a rising interest in wood, it is of great importance to enhance the knowledge of its burning behaviour in order to predict and prevent fire hazards. Fire development is often characterized in terms of heat release rate (HRR) as a function oftime. Therefore, HRR is considered one of the most important variables in the evaluation of material fire hazards. This study aims to generate greater knowledge of the HRR curve of wood when exposed to heating in the cone calorimeter and how the curve can be described quantitatively. Furthermore, it was attempted to comprehend the properties and functions of char and its effects on HRR during combustion. The study is based on laboratory tests carried out with a cone calorimeter and a Scanning Electron Microscope (SEM). The cone calorimeter was set to generate a heat flux of 35 kWm-2. Spruce wood samples of three thicknesses were analysed, namely 10, 20 and 30mm. The samples were assembled with one of three types of material on the rear side of the samples, which were Kaowool, steel plates and aluminium foil wrapped around wood. The different materials were used as they are greatly dissimilar in their thermal properties. Wood with both low and normal moisture content was also analysed. Char was analysed with SEM. The results show that there are four major points of interest in the HRR curve of wood. The first point is the initial peak heat release rate (PHRR) that occurs when the sample surface ignites causing great production of heat which increases the HRR. The second point of interest is the vast decrease in HRR soon after the first PHRR, this is due to char formation, which acts as a protective barrier preventing the exchange of volatile gases and oxygen. The third point of interest is a second PHRR close to the end of the combustion that occurs as a response to sample burn through, which means that the heat gradient reaches the rear side of the sample. The second PHRR is highly dependent on the boundary condition defined by the rear material, which determines the heat losses at the rear side of the specimen, and consequently the temperature of the specimen. The higher is the specimen temperature, the higher is the pyrolysis rate, and therefore also the higher the second PHRR. Moreover, high moisture content delays the time of occurrence of the second PHRR as more water needs to undergo phase change, which requires a high amount of energy. The final point of interest is the final decrease in HRR as a result of fuel depletion leading to the sample smouldering or the fire being extinguished. Char, formed by mainly lignin and some cellulose in wood, affects the overall HRR. The SEM analysis showed that the char cracks grew wider during the second PHRR. It is, however, observed that char cracking has no significance in the time of occurrence of the second PHRR as this is based on sample burn through, and it was difficult to determine to what extent char cracking affected the intensity of the PHRR. This systematic study is considered adequate to justify the research questions and aim of this study. It has also created new questions for further study in the area as well as provided a deeper understanding of the fundamental burning behaviour of wood. / Klimatförändringen och dess medföljande miljöfrågor har fått byggbranschen att använda mer hållbara och miljövänliga byggmaterial. Trä har alltid varit ett byggmaterial men på grund av ett förnyat intresse för hållbarhet och förnybarhet har användningen av materialet ökat under de senaste åren. Med ett stigande intresse för trä är det av stor vikt att öka kunskapen om dess förbränningsbeteende för att kunna förutse och förebygga brandrisker. Brandutveckling karakteriseras ofta i termer av värmeavgivningshastighet (HRR) som funktion av tid. Det är därför en av de viktigaste variablerna i utvärderingen av brandrisker. Denna studie syftar till att skapa större kunskap om HRR-kurvan för trä när det utsätts för värme i konkalorimetern och hur kurvan kan beskrivas kvantitativt. Vidare, att studera kollagrets egenskaper och funktioner samt hur det påverkar HRR under förbränning. Studien bygger på laborativa försök utförda med en konkalorimeter och ett svepelektronmikroskop (SEM). Konkalorimetern genererade strålning med intensitet 35 kWm-2. Tre tjocklekar av granprover testades, 10, 20 och 30 mm. Proverna placerades ovanpå en av tre typer av material i en provform, Kaowool, stålplattor och trä invirat i aluminiumfolie. Materialen användes då deras termiska egenskaper skiljer sig åt. Vidare testades även trä av både låg och normal fukthalt. Kollagret analyserades med SEM. Resultatet visar att det finns fyra intressanta områden på HRR-kurvan för trä. Det första är den initiala maximala värmeavgivningshastigheten (PHRR) som inträffar när provytan antänder vilket orsakar en stor värmeproduktion som ökar HRR. Det andra är en kraftig minskning av HRR strax efter den första PHRR. Detta beror på att kol börjat bildas på provytan, kollagret fungerar som en skyddande barriär som förhindrar utbyte av flyktiga gaser och syre. Det tredje är en andra PHRR som inträffar nära brandprovets slut. Detta sker till följd av provkroppsgenombränning som innebär att värmegradienten når provets baksida. Intensitetenav PHRR är starkt beroende av materialet bakom provet. Det bestämmer värmeförlusten på provets baksida och därmed även provkroppens temperatur. Ju högre provkroppstemperaturenär, desto högre är pyrolyshastigheten vilket leder till en högre andra PHRR. Hög fukthalt fördröjer även tidpunkten för uppkomsten av den andra PHRR eftersom fasomvandling av vatten kräver en stor mängd energi. Det sista och fjärde området av intresse är en minskning av HRR efter den andra PHRR, detta sker när allt bränsle förbränts och det som kvarstår är endast ett glödande prov. Kollagret, som främst bildas av lignin och en del cellulosa i träet, påverkar den totala HRR. SEM-analysen visade att sprickorna i kollagret blev bredare under den andra PHRR. Däremot observerades det att sprickbildningen inte har någon betydelse för tidpunkten av den andra PHRR uppkomst då denna enbart är baserad på provets genombränning. Det är även svårt att avgöra i vilken utsträckning sprickbildningen påverkar intensiteten av PHRR. Metoden som används för att besvara frågeställningarna och syftet anses vara adekvat. Studien har öppnat upp för ytterligare frågeställningar och idéer till fortsatta försök inom området. Vidare har även studien gett en djupare förståelse om förbränningsbeteendet av trä.

CO, volatile organic compounds, and polyaromatics areubiquitous air pollutants that give rise to deleterious healthand environmental effects. Such compounds are emitted, forinstance, by the combustion of wood, particularly fromsmall-scale heating appliances. Total catalytic oxidation isconsidered to be an effective approach in controlling theseemissions, however, some problems remain such as thenon-availability of catalysts with low-cost, high activity andstability in prevailing conditions. Hence, this thesis aims atthe development of oxidation catalysts and improvedunderstanding of their behaviour. The catalytic activity was evaluated for the oxidation of amixture of CO, naphthalene (or ethylene), and methane inpresence of carbon dioxide, water, oxygen and nitrogen. Variouscharacterisation techniques, including Temperature-ProgrammedReduction and Oxidation, BET-Surface Area Analysis, X-RayDiffraction, X-Ray Photoelectron Spectroscopy, RamanSpectroscopy and Scanning and Transmission Electron Microscopywere used. In the first part of this thesis, catalysts based on metaloxides (MnOx, CuO) and/or a low amount of noble metals (Pt, Pd)supported on alumina washcoat were selected. It was shown thatPt and Pd possessed a superior catalytic activity to that ofCuO and MnOxfor the oxidation of CO, C10H8and C2H4, while for the oxidation of CH4, CuO was largely more active than noble metals,and MnOxas active as Pd and Pt. Some mixed metaloxide-noble metal catalysts showed decreased activity comparedto that of noble metals, however, a higher noble metal loadingor a successive impregnation with noble metals led to positivesynergetic effects for oxidation. Deactivation of the catalysts by thermal damage and sulphurpoisoning is addressed in the second part of the dissertation.An alumina washcoat was found to be well anchored to themetallic support after thermal treatment at 900°C due tothe growth of alumina whiskers. The sintering of the washcoatwas accelerated after high temperature treatments in thepresence of metal catalysts. In addition, alumina was found toreact with CuO, particularly in presence of noble metals at900°C, to form inactive CuAl2O4. However, MnOxcatalyst benefits from the more active Mn3O4phase at high temperature, which makes it asuitable active catalyst for the difficult oxidation of CH4. Pt sintering was delayed when mixed with CuO,thus giving more thermally resistant catalyst. The mixed metaloxide-noble metal catalysts showed higher activity afterpre-sulphation of the catalysts with 1000 ppm SO2in air at 600°C or during activitymeasurement in presence of 20 ppm SO2in the gas mixture, compared to single componentcatalysts. In some cases, the activities of the mixed catalystswere promoted by pre-sulphation due to the presence of sulphatespecies. Thermal stabilisation of the catalytic componentsand thealumina by promotion of La in the washcoat is discussed in thethird section. The stabilising effect of La at high temperatureis also compared to that of Ce added in the catalysts for otherpurposes. Due to its better dispersion, La contributed to thethermal stabilisation of the alumina washcoat and its activecomponents to a higher extent than Ce did. La provided a betterdispersion and a higher saturation of metal oxides in thealumina support, and at the same time stabilised the activityof the catalysts by preventing undesirable solid-phasereactions between metal oxide and alumina. In addition, La wasfound to enhance the dispersion and the oxygen mobility of CeO2. Cu-Ce interactions were found to promotesubstantially the CO oxidation due to an increase of thestability and reducibility of Cu species. Synergetic effectswere also found between Ce and La in the washcoat of CuO-Ptcatalyst, which facilitated the formation of reduced Pt and CeO2, thus enhancing significantly the catalyticactivity compared to that of a Pt only catalyst. The last part was an attempt to demonstrate the potential ofa catalyst equipped with a pre-heating device in a full-scalewood-fired boiler for minimising the high emissions during thestart-up phase. During the first ten minutes of the burningcycle a significant reduction of CO and hydrocarbons wereachieved. <b>Keywords</b>: wood combustion, catalysts, total oxidation,manganese, copper, platinum, palladium, lanthanum, cerium, CO,VOC, methane, deactivation, thermal stability, sulphurdioxide.

<p>CO, volatile organic compounds, and polyaromatics areubiquitous air pollutants that give rise to deleterious healthand environmental effects. Such compounds are emitted, forinstance, by the combustion of wood, particularly fromsmall-scale heating appliances. Total catalytic oxidation isconsidered to be an effective approach in controlling theseemissions, however, some problems remain such as thenon-availability of catalysts with low-cost, high activity andstability in prevailing conditions. Hence, this thesis aims atthe development of oxidation catalysts and improvedunderstanding of their behaviour.</p><p>The catalytic activity was evaluated for the oxidation of amixture of CO, naphthalene (or ethylene), and methane inpresence of carbon dioxide, water, oxygen and nitrogen. Variouscharacterisation techniques, including Temperature-ProgrammedReduction and Oxidation, BET-Surface Area Analysis, X-RayDiffraction, X-Ray Photoelectron Spectroscopy, RamanSpectroscopy and Scanning and Transmission Electron Microscopywere used.</p><p>In the first part of this thesis, catalysts based on metaloxides (MnO_x, CuO) and/or a low amount of noble metals (Pt, Pd)supported on alumina washcoat were selected. It was shown thatPt and Pd possessed a superior catalytic activity to that ofCuO and MnO_xfor the oxidation of CO, C₁₀H₈and C₂H₄, while for the oxidation of CH₄, CuO was largely more active than noble metals,and MnO_xas active as Pd and Pt. Some mixed metaloxide-noble metal catalysts showed decreased activity comparedto that of noble metals, however, a higher noble metal loadingor a successive impregnation with noble metals led to positivesynergetic effects for oxidation.</p><p>Deactivation of the catalysts by thermal damage and sulphurpoisoning is addressed in the second part of the dissertation.An alumina washcoat was found to be well anchored to themetallic support after thermal treatment at 900°C due tothe growth of alumina whiskers. The sintering of the washcoatwas accelerated after high temperature treatments in thepresence of metal catalysts. In addition, alumina was found toreact with CuO, particularly in presence of noble metals at900°C, to form inactive CuAl₂O₄. However, MnO_xcatalyst benefits from the more active Mn₃O₄phase at high temperature, which makes it asuitable active catalyst for the difficult oxidation of CH₄. Pt sintering was delayed when mixed with CuO,thus giving more thermally resistant catalyst. The mixed metaloxide-noble metal catalysts showed higher activity afterpre-sulphation of the catalysts with 1000 ppm SO₂in air at 600°C or during activitymeasurement in presence of 20 ppm SO₂in the gas mixture, compared to single componentcatalysts. In some cases, the activities of the mixed catalystswere promoted by pre-sulphation due to the presence of sulphatespecies.</p><p>Thermal stabilisation of the catalytic componentsand thealumina by promotion of La in the washcoat is discussed in thethird section. The stabilising effect of La at high temperatureis also compared to that of Ce added in the catalysts for otherpurposes. Due to its better dispersion, La contributed to thethermal stabilisation of the alumina washcoat and its activecomponents to a higher extent than Ce did. La provided a betterdispersion and a higher saturation of metal oxides in thealumina support, and at the same time stabilised the activityof the catalysts by preventing undesirable solid-phasereactions between metal oxide and alumina. In addition, La wasfound to enhance the dispersion and the oxygen mobility of CeO₂. Cu-Ce interactions were found to promotesubstantially the CO oxidation due to an increase of thestability and reducibility of Cu species. Synergetic effectswere also found between Ce and La in the washcoat of CuO-Ptcatalyst, which facilitated the formation of reduced Pt and CeO₂, thus enhancing significantly the catalyticactivity compared to that of a Pt only catalyst.</p><p>The last part was an attempt to demonstrate the potential ofa catalyst equipped with a pre-heating device in a full-scalewood-fired boiler for minimising the high emissions during thestart-up phase. During the first ten minutes of the burningcycle a significant reduction of CO and hydrocarbons wereachieved.</p><p><b>Keywords</b>: wood combustion, catalysts, total oxidation,manganese, copper, platinum, palladium, lanthanum, cerium, CO,VOC, methane, deactivation, thermal stability, sulphurdioxide.</p>

This diploma thesis deals with issues of fine and ultrafine particles formation during thermal decomposition and combustion of biomass. An introduction is devoted to a utilization of biomass as fuel. A following part describes the gas products emerging generally during combustion process. A current emission and air pollution situation in the Czech Republic as well as the health impacts of solid pollutants on human are also mentioned. Within an experimental measurement three basic factors that have impact on fine particles formation during combustion of beech wood (i. e. oxygen content in combustion atmosphere, type of the sample and size of the sample) were thoroughly analyzed. Attention was paid to a progress of thermal decomposition and combustion of sample with respect to the particles formation. Finally, a measurement of fine particles amount was accomplished in a real boiler successively with four different biomass pellet types.

Concentrations of CO, CO₂, and O₂ in woodstove flue gases are some of the measured inputs required by algorithms used to calculate woodstove efficiency by the stack loss method. Since these algorithms have been shown to be very sensitive to small errors in these input values, it was necessary to determine whether measurements of these compounds are subject to interference. Concentrations of CO, CO₂, and O₂ in a series of flue gas samples were measured using a variety of independent measurement techniques for each compound. The concentrations indicated by each of the measurement techniques for each compound and sample were compared to check for agreement. Disagreement among the measurement techniques for a given compound could indicate interference if some trend could be established. Tests were conducted on four samples taken randomly during each of three stove firings. / M.S.

<p>Wood combustion is mainly used in cold regions as a primary or supplemental space heating source in residential areas. In several industrialized countries, there is a renewed interest in residential wood combustion (RWC) as an alternative to fossil fuel and nuclear power consumption. The main objective of this thesis was to investigate the impact of RWC on the air quality in urban areas. To this end, a field campaign was conducted in Northern Sweden during wintertime to characterize atmospheric aerosol particles and polycyclic aromatic hydrocarbons (PAH) and to determine their source apportionment.</p><p>A large day-to-day and hour-to-hour variability in aerosol concentrations was observed during the intensive field campaign. On average, total carbon contributed a substantial fraction of PM10 mass concentrations (46%) and aerosol particles were mostly in the fine fraction (PM1 accounted for 76% of PM10). Evening aerosol concentrations were significantly higher on weekends than on weekdays which could be associated to the use of wood burning for recreational purposes or higher space heat demand when inhabitants spend longer time at home. It has been shown that continuous aerosol particle number size distribution measurements successfully provided source apportionment of atmospheric aerosol with high temporal resolution. The first compound-specific radiocarbon analysis (CSRA) of atmospheric PAH demonstrated its potential to provide quantitative information on the RWC contribution to individual PAH. RWC accounted for a large fraction of particle number concentrations in the size range 25-606 nm (44-57%), PM10 (36-82%), PM1 (31-83%), light-absorbing carbon (40-76%) and individual PAH (71-87%) mass concentrations.</p><p>These studies have demonstrated that the impact of RWC on air quality in an urban location can be very important and largely exceed the contribution of vehicle emissions during winter, particularly under very stable atmospheric conditions.</p>

Wood combustion is mainly used in cold regions as a primary or supplemental space heating source in residential areas. In several industrialized countries, there is a renewed interest in residential wood combustion (RWC) as an alternative to fossil fuel and nuclear power consumption. The main objective of this thesis was to investigate the impact of RWC on the air quality in urban areas. To this end, a field campaign was conducted in Northern Sweden during wintertime to characterize atmospheric aerosol particles and polycyclic aromatic hydrocarbons (PAH) and to determine their source apportionment. A large day-to-day and hour-to-hour variability in aerosol concentrations was observed during the intensive field campaign. On average, total carbon contributed a substantial fraction of PM10 mass concentrations (46%) and aerosol particles were mostly in the fine fraction (PM1 accounted for 76% of PM10). Evening aerosol concentrations were significantly higher on weekends than on weekdays which could be associated to the use of wood burning for recreational purposes or higher space heat demand when inhabitants spend longer time at home. It has been shown that continuous aerosol particle number size distribution measurements successfully provided source apportionment of atmospheric aerosol with high temporal resolution. The first compound-specific radiocarbon analysis (CSRA) of atmospheric PAH demonstrated its potential to provide quantitative information on the RWC contribution to individual PAH. RWC accounted for a large fraction of particle number concentrations in the size range 25-606 nm (44-57%), PM10 (36-82%), PM1 (31-83%), light-absorbing carbon (40-76%) and individual PAH (71-87%) mass concentrations. These studies have demonstrated that the impact of RWC on air quality in an urban location can be very important and largely exceed the contribution of vehicle emissions during winter, particularly under very stable atmospheric conditions.