This diploma thesis deals with the use of CO2 in gasification of biomass. The theoretical part is focus on description of gasification process and gasification reactors. The next part descripes the influence of the gasifitation medium composition on the properties of the generated gas. The experimental part is devoted to gasification of biomass on a fluidized bed generator, where the effect of CO2 concetration in the gasification medium on the properties of the generated gas is investigated. In the final part is the evaluation of the results.

This thesis aims to gas installation of the coal boiler and its thermal recount. In the first part, there is implemented calculation of the combusting chamber. After that follows the recalculation of heat exchange surfaces and proposal tube air heater, which will replace the existing air heater Ljungström. The emphasis is placed on the preservation of the exsiting steam parametrs and keeps emission limit of NOx.

This masters thesis deals with the gasification of current oil boiler. The first part of the thesis describes the existing boiler. The next part follows gasification with respect for comply with the limits of NOX and recalculation of boiler for operation with the natural gas.

This investigation provides a comprehensive experimental dataset and kinetic model for biomass gasification, over a wide temperature range (1150-1350 °Ï¹) in CO2, H2O and the combination of these two reactant gases over the mole fraction ranges of 0 to 0.5 for H2O and 0 to 0.9 for CO2. The data come from a unique experimental facility that tracks continuous mass loss rates for poplar wood, corn stover and switchgrass over the size range of 6-12.5 mm. In addition, the data include char size, shape, surface and internal temperature and discrete measurements of porosity, total surface area, pore size distribution and composition. This investigation also includes several first-ever observations regarding char gasification that probably extend to char reactivity of all types and that are quantified in the model. These include: the effect of ash accumulation on the char surface slowing the apparent reaction rate, changes in particle size, porosity and density as functions of burnout, and reaction kinetics that account for all of these changes. Nonlinear least-squares regression produces optimized power-law model parameters that describe gasification with respect to both CO2 and H2O separately and in combination. A single set of parameters reasonably describes rates for all three chars. Model simulations agree with measured data at all stages of char conversion. This investigation details how ash affects biomass char reactivity, specifically the late-stage burnout. The ash contents ratios in the raw fuels in these experiments are as high as 40:1, providing a clear indication of the ash effect on the char reactivity. The experimental results definitively indicate a decrease in char reaction rate with increasing initial fuel ash content and with increasing char burnout -- most pronounced at high burnout. This investigation postulates that an increase in the fraction of the surface covered by refractory material associated with either higher initial ash contents or increased burnout decreases the surface area available for reaction and thus the observed reaction rate. A quantitative model that includes this effect predicts the observed data at any one condition within the data uncertainty and over a broad range of fuel types, particle sizes, temperatures, and reactant concentrations slightly less accurately than the experimental uncertainty. Surface area, porosity, diameter, and density predictions from standard models do not adequately describe the experimental trends. Total surface area increases slightly with conversion, with most of the increase in the largest pores or channels/vascules not measurable by standard surface area techniques but most of the surface area is in the small pores. Porosity also increases with char conversion except for abrupt changes associated with char and ash collapse at the end of char conversion. Char particle diameters decrease during these kinetically controlled reactions, in part because the reaction is endothermic and therefore proceeds more rapidly at the comparatively warmer char surface. SEM images qualitatively confirm the quantitative measurements and imply that the biomass microstructure does not appreciably change during conversion except for the large pore diameters. Extant char porosity, diameter, surface area, and related models do not predict these trends. This investigation suggests alternative models based on these measurements.

Historically, fossil fuel sources (coal, oil and natural gas) have played significant role in meet global energy demand. As global population continue to rise, more and more energy resources are needed and there is a continuous depletion of these energy resources. The prices of these fuels have often fluctuated over the years and this has greatly affected the economy of several nations. The use of these fossil-based fuels has had enormous impact on the environment. This is as a result carbon dioxide and other greenhouse gases emissions. Many nations are continuously showing great interest and efforts to work together to address some of these issues, for example, the global response to combat climate change (Paris Agreement), which has been ratified by over 188 states. There is a growing interest in the technological development of renewable sources like biomass, in the production of heat, electricity and synthetic fuels. The renewable energy consumption target by the European union, stands at 32%, with a minimum of 14% in the road and transport sector. Sweden as a member state, has made tremendous progress in reducing its dependence on fossil fuels and increase its use of renewables (particularly biomass) over the years. Sweden has a target to reduce its CO2 emission in the transport sector by 79% and an independence of fossil fuels in its vehicle fleets by 2030. The thermochemical conversion of biomass to hydrogen, to power hydrogen fuel cell vehicles, has been suggested as one route to achieve this target. Biomass has high volatile content and the kinetics and stoichiometry of thermochemical conversion is very complex. This study evaluates the feasibility of a 300 kW hydrogen pilot scale production unit from biomass (wood pellet) in Växjö. Mass and energy balance calculations were performed, mainly in the first two reactors, in the envisage design and the lower heating value of the product gas was determined. Data that were used for this study was gotten from the plant in Växjö, literature survey of related systems and tools that were used to facilitate the calculations include Microsoft Excel and HSC chemistry for equilibrium calculations. The result of mass and energy balance analysis on the 1MW fuel feeding system, showed that, the flow rate of sand required for the pyrolysis process (700°) is 2610 kg/h, and the energy of pyrolysis equals 217 MJ/h. Partial burning of the pyrolysis gas in the secondary reactor produces product gas consisting of mainly CO, CO2 H2 and H2O with volume percent equal 47.08%, 6.94%, 30.29% and 15.69% respectively. The calculated lower heating value of this gas is 9.04 MJ/Nm3 when pure oxygen was used in partial burning of pyrolysis gas and approximately 6.0 MJ/Nm3 when air was used for burning. The 1MW fuel (wood pellet) feeding via thermochemical conversion has a production potential of 229 kW of hydrogen gas. Based on the parameters considered in this thermochemical process, the calculated Cold Gas Efficiency equal 59.7% and a Carbon Conversion Efficiency equal to 70.3%.

This project focuses on the numerical modeling of a rotary kiln pyrolyzer such as found in the e.g. WoodRoll multistage gasification process. The model consists of two parts: a granular flow model, and a pyrolyzer model. In the first part, Saeman's equation was employed to develop a model which can describe the behavior of solid granular flow in a rotary kiln without reaction. Residence-time distribution (RTD) is the main aim to study in this part, which was simulated by axial dispersion model (ADM). The model requires only one fitting parameter that is dispersion coefficient (Dax), which was studied in parallel by two cases: constant value of Dax, and Dax as a function of kiln's length. The result of both models show good predictable in comparison to experimental data from literature, and represent narrow distribution of residence times that behave similar to plug flow reactor. Unfortunately, the result still cannot claim which model of Dax is the best model to describe RTD in rotary drum. The second part of the thesis purpose to design the model of rotary kiln pyrolyzer, which contains specific behavior of granular flow, heat transport in a kiln, and primary pyrolysis of wood. The model of steady-state condition with constant wall temperature was simulated to generate temperature profile and conversion along a kiln. This model included all heat transport features such as conduction, convection, and radiation. According to the result, supplied energy from outer surface of the kiln essentially transfer through the kiln via heat conduction, which occur between solid bed and rotating surface of the kiln. Temperature profile that generated by this model looks reasonable to the process of rotary kiln pyrolyzer, which affected by heating system and heat of reaction along the kiln. The result also demonstrated that conversion of wood is strongly dependent of wall temperature or heating rate of the system. Nonetheless, kinetics data for wood pyrolysis still a debatable issue in many research, and this model required validation by experiment of rotary kiln pyrolyzer.

This investigation provides a comprehensive experimental dataset and kinetic model for biomass gasification, over a wide temperature range (1150-1350 °Ï¹) in CO2, H2O and the combination of these two reactant gases over the mole fraction ranges of 0 to 0.5 for H2O and 0 to 0.9 for CO2. The data come from a unique experimental facility that tracks continuous mass loss rates for poplar wood, corn stover and switchgrass over the size range of 6-12.5 mm. In addition, the data include char size, shape, surface and internal temperature and discrete measurements of porosity, total surface area, pore size distribution and composition. This investigation also includes several first-ever observations regarding char gasification that probably extend to char reactivity of all types and that are quantified in the model. These include: the effect of ash accumulation on the char surface slowing the apparent reaction rate, changes in particle size, porosity and density as functions of burnout, and reaction kinetics that account for all of these changes. Nonlinear least-squares regression produces optimized power-law model parameters that describe gasification with respect to both CO2 and H2O separately and in combination. A single set of parameters reasonably describes rates for all three chars. Model simulations agree with measured data at all stages of char conversion. This investigation details how ash affects biomass char reactivity, specifically the late-stage burnout. The ash contents ratios in the raw fuels in these experiments are as high as 40:1, providing a clear indication of the ash effect on the char reactivity. The experimental results definitively indicate a decrease in char reaction rate with increasing initial fuel ash content and with increasing char burnout -- most pronounced at high burnout. This investigation postulates that an increase in the fraction of the surface covered by refractory material associated with either higher initial ash contents or increased burnout decreases the surface area available for reaction and thus the observed reaction rate. A quantitative model that includes this effect predicts the observed data at any one condition within the data uncertainty and over a broad range of fuel types, particle sizes, temperatures, and reactant concentrations slightly less accurately than the experimental uncertainty. Surface area, porosity, diameter, and density predictions from standard models do not adequately describe the experimental trends. Total surface area increases slightly with conversion, with most of the increase in the largest pores or channels/vascules not measurable by standard surface area techniques but most of the surface area is in the small pores. Porosity also increases with char conversion except for abrupt changes associated with char and ash collapse at the end of char conversion. Char particle diameters decrease during these kinetically controlled reactions, in part because the reaction is endothermic and therefore proceeds more rapidly at the comparatively warmer char surface. SEM images qualitatively confirm the quantitative measurements and imply that the biomass microstructure does not appreciably change during conversion except for the large pore diameters. Extant char porosity, diameter, surface area, and related models do not predict these trends. This investigation suggests alternative models based on these measurements.

Using biomass gasification to produce combustible gas is one of the promising sustainable energy optionsavailable for many countries. At present, a few small scale community based power generation systemsusing biomass gasifiers are in operation in Sri Lanka. However, due to the lack of proper knowledge, thesesystems are not being operated properly in full capacity. This stands as an obstacle for further expansionof the use of gasifier technology.The objective of this study was to identify the most influential parameters related to fuel wood gasificationwith a down draft gasifier in order to improve the gasification processes.A downdraft gasifier of 10kW electrical capacity was used to study the effect of equivalent ratio (Actual airfuel ratio to Stoicheometric air fuel ratio: ER) on the specific gas production, the heating value of gasproduced and the cold gas efficiency using three throat diameters (125mm, 150mm and 175mm). Six trialswere carried out for each throat diameter by varying the supply air flow to change the ER. The gassamples were tested for their compositions under steady state operating conditions. Using mass balancesfor C and N, the cold gas efficiencies, calorific values and the specific gas production rates weredetermined.The results showed that with all throat diameters the calorific value of gas reduced with the increase ofER. The cold gas efficiency reduced with ER in a similar trend for all three throat diameters. The specificgas production increased with ER under all throat diameters.Calorific value and specific gas production are changing inversely proportional manner. The ER to beoperated is depends on the type of application of the gas produced and engine characteristics. When alarge heat is required, low ER is to be used in which gas production is less. In the opposite way, when alarge amount of gas is needed, higher value of ER is recommended.

In recent years, third-generation--or algae-based biofuels--have been studied extensively in order to reduce the risks of compromised food security, solve biofuel issues from past generations and supply continuous feedstock from energy crops. With the goal of a zero-carbon future, bioenergy with carbon capture and storage (BECCS) is a technology that extends to multiple areas--including algae-based biofuels that avoid greenhouse emissions from biomass processing. Algae are aquatic plants or microorganisms, classified as micro and macroalgae; they are of considerable scientific interest because they are fast-growing, with a photosynthetic metabolism that generates carbon sources from atmospheric CO$_2$. Macroalgae (seaweed) can be cultivated in aquaculture farms and collected through mechanical devices; the macroalga selected for this study is Macrocystis pyrifera, a giant brown seaweed characterized by its size and its carbon and oxygen-rich composition. Conventional methods for thermal conversion into potential fuels, such as biomass carbonization, pyrolysis, and gasification are not efficient for biomass with high moisture. For this reason, the research community has introduced new methods like hydrothermal carbonization, liquefaction, and gasification. This project focuses on the process simulation in Aspen plus® V12 to produce green hydrogen from macroalgae biomass by pyrolysis, gasification, and hydrothermal gasification. Hydrogen production was maximized through sensitivity analysis, achieving a hydrogen yield of 2.08% in hydrothermal gasification, 2.06% for pyrolysis, and 1.85% for gasification.

This work is dealing with the utilization of biomass feed stocks and wooden residue for gasification process to produce syn-gas suitable for the implementation of power plants for electricity generation and problem of gas production suitable for further chemical and energy purpose discussing the suitable practical purification methods, given that the complexity of theme and project which carried out through detailed analysis. Since the obtained gas has many types of unwanted contaminants. It was necessary to derive an effective cleaning method for gas purification from chemical contaminants especially tars components. The discussion of the definitions and methods for the determination of gas unwanted components and their removal technologies on the basis of the knowledge of data, collecting and analysis carried out through an experimental massive approach. The theoretical analysis of the gasification process for an effective tar reduction in the produced gas has been studied as well. Since the quality requirements for internal combustion engines, gas turbines and fuel cells using the primary measurement methods cannot be achieved for gas production, this work aimed removing different particulates and tar. The main emphasis is placed on the methods of high cleaning taking in account the chemical and thermal specifications of the gas which is based on the utilization of three different kinds of carbon materials successfully and efficiently char coal, black coke and active carbon for tar removal which has a major impact on the process parameters. The analysis was responding with the mechanism and the techniques of minimizing the resultant allowable concentration by using a suitable materials and verifying the operation conditions without affecting the gas thermal efficiency. The highlights of the theoretical and experimental work has been drawn up by a high concept cleaning allowing the production of a pure gas having a quality that meets the modern technical requirements for electricity generation. Functionality the most efficient cleaning methods were based in the current project for tar reduction on the quantity of tar removed, the materials used for tar cracking and the conditions of the experimental work as well. For a successful application, some proposals have been settled for industrial applications of gas cleaning.