Tesi sul tema "Gasifiers"
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1
Duchesne, Marc A. "Slagging in Entrained-flow Gasifiers". Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/23353.
Testo completoAbstract (sommario):
Gasification is a flexible technology which is applied in industry for electricity generation, hydrogen production, steam raising and liquid fuels production. Furthermore, it can utilize one or more feedstocks such as coal, biomass, municipal waste and petroleum coke. This versatility, in addition to being adaptable to various emissions control technologies (including carbon capture) renders it an attractive option for years to come. One of the most common gasifier types is the entrained-flow slagging gasifier. The behaviour of inorganic fuel components in these gasifiers is still ill-understood even though it can be the determining factor in their design and operation. A literature review of inorganic matter transformation sub-models for entrained-flow slagging gasifiers is provided. Slag viscosity was identified as a critical property in the sub-models. Slag viscosity models are only applicable to a limited range of slag compositions and conditions, and their performance is not easily assessed. An artificial neural network model was developed to predict slag viscosity over a broad range of temperatures and slag compositions. Furthermore, a toolbox was developed to assist slag viscosity model users in the selection of the best model for given slag compositions and conditions, and to help users determine how well the best model will perform. The slag viscosities of coal, petroleum coke and coal/petroleum coke blends were measured in the temperature range of 1175-1650ºC. Interaction of vanadium-rich slags with various materials was investigated. The results from the first two parts of a three-part research program which involves fuel characterization, testing in a 1 MWth gasifier, and computational fluid dynamics (CFD) modeling for entrained-flow slagging gasification are presented. The end goal is to develop a CFD model which includes inorganic matter transformations. Fuel properties were determined with prioritization based on their application; screening of potential fuels, ensuring proper gasifier operation, gasifier design and/or CFD modeling. Using CanmetENERGY’s 1 MWth gasifier, five gasification tests were completed with the characterized coals. Solid samples from the refractory liners, in-situ gas sampling probe sheaths and impingers, the slag tap, the slag pot, quench discharge water and scrubber water were collected and characterized.
2
Latif, Ajmal. "A study of the design of fluidized bed reactors for biomass gasification". Thesis, University College London (University of London), 1999. http://discovery.ucl.ac.uk/1349342/.
Testo completoAbstract (sommario):
The present study is in two parts, the first part describes an investigation that was undertaken to determine the feasibility and hydrodynamic behaviour of a cold model circulating fluidized bed system proposed for the continuous combustion-gasification of biomass. The design is based on the principle that the char produced in the gasifier is circulated with the bed material and combusted in a separate reactor to generate the heat required for the gasification process. While high solid circulation rates are required to maintain the heat balance, product and flue gas mixing between the two units must be minimised or eliminated. The design of the circulating bed simply consists of two fluid bed units connected two together via a riser and a downcomer fitted with a non-mechanical valve. Various aspects such as solid circulation rate, gas mixing, solids mixing, and pressure component around the circulating loop were studied. Results show that the solid circulation and gas mixing are strongly influenced by the riser gas velocity, total solids inventory, and position of the riser from the riser gas jet. Solid circulation fluxes of up to 1 l5kg/m 2s were attained and easily controlled. The flue gas crossflow was less than 4% over the range studied. By analysing the experimental data, a series of mathematical correlations were obtained which successfully predict the exponential relationship that exists between the solid circulation rate, gas mixing and the operating parameters. The potential of this system for its purpose is highlighted. The second part of the study focuses on the design and development of a heated fluidized bed reactor with an on-line gas and solids sampling technique to study the steam gasification of biomass (almond shells). Experiments were conducted at temperatures of up to 800°C to investigate the gasification rates of biomass char under different operating conditions. Understanding the gasification and combustion rates of biomass char is an important step towards the proper designing of biomass gasifiers. In the heated fluid bed, the extent of the gasification of biomass increased with increasing temperature as indicated by an increase in the quantity of gaseous products. A hydrogen content of up to 43% by volume was obtained. The sampling technique adopted allows the collection of the bed sample at gasification conditions which can be used to predict the composition of the bed. The gasification rate of biomass (almond shell) char was found to be affected by the gasification temperature. In order to evaluate the char gasification rate constants, the shrinking core model with reaction controlling step (SCM) was applied to the char gasification data. The rate constant values obtained from the SCM were 5.14E-5, 7.67E- 5, and 1.26E-4 s' for temperatures of 712, 753, and 806 °C respectively. The activation energy was evaluated as 89 kJ/mol. These values were in close agreement with those published in the literature. SEM pictures of the surface of the chars shows that at high temperatures, the char formed is very porous and hence very reactive. With regards to practical gasifiers, the results obtained have been used to evaluate an --mum volume for a typical biomass gasifier operating at 850 °C. The aim of the present work were satisfactorily achieved.
3
Monaghan, Rory F. D. (Rory Francis Desmond). "Dynamic reduced order modeling of entrained flow gasifiers". Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/58191.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references.
Gasification-based energy systems coupled with carbon dioxide capture and storage technologies have the potential to reduce greenhouse gas emissions from continued use of abundant and secure fossil fuels. Dynamic reduced order models (ROMs) that predict the operation of entrained flow gasifiers (EFGs) within IGCC (integrated gasification combined cycle) or polygeneration plants are essential for understanding the fundamental processes of importance. Such knowledge can be used to improve gasifier reliability, availability and maintainability, leading to greater commercialization of gasification technology. A dynamic ROM, implemented in Aspen Custom Modeler, has been developed for a range of EFGs. The ROM incorporates multiple feedstocks, mixing and recirculation, particle properties, drying and devolatilization, chemical kinetics, fluid dynamics, heat transfer, pollutant formation, slag behavior and syngas cooling. The ROM employs a reactor network model (RNM) that approximates complex fluid mixing and recirculation using a series of idealized chemical reactors. The ROM was successfully validated for steady-state simulation of four experimental gasifiers. The throughputs of these gasifiers range from 0.1 to 1000 metric tonnes per day (3 kWth - 240 MWth). Sensitivity analysis was performed to identify the parameters most important to ROM accuracy. The most important parameters are found to be those that determine RNM geometry, particle physical and kinetic properties, and slagging. The ROM was used to simulate the steady-state and dynamic performance of a full-scale EFG system. In steady-state mode, the ROM was used to establish base case and fluxant requirements. The base case performance agreed with design specifications. Steady-state simulation was also used to determine important states for dynamic simulation. Six cases were examined in dynamic mode, including gasifier cold start. Dynamic results showed agreement with industrial experience for gasifier start-up times.
by Rory F. D. Monaghan.
Ph.D.
4
Double, J. M. "The design, evaluation and costing of biomass gasifiers". Thesis, Aston University, 1988. http://publications.aston.ac.uk/9702/.
Testo completoAbstract (sommario):
The objective of this study has been to enable a greater understanding of the biomass gasification process through the development and use of process and economic models. A new theoretical equilibrium model of gasification is described using the operating condition called the adiabatic carbon boundary. This represents an ideal gasifier working at the point where the carbon in the feedstock is completely gasified. The model can be used as a `target' against which the results of real gasifiers can be compared, but it does not simulate the results of real gasifiers. A second model has been developed which uses a stagewise approach in order to model fluid bed gasification, and its results have indicated that pyrolysis and the reactions of pyrolysis products play an important part in fluid bed gasifiers. Both models have been used in sensitivity analyses: the biomass moisture content and gasifying agent composition were found to have the largest effects on performance, whilst pressure and heat loss had lesser effects. Correlations have been produced to estimate the total installed capital cost of gasification systems and have been used in an economic model of gasification. This has been used in a sensitivity analysis to determine the factors which most affect the profitability of gasification. The most important influences on gasifier profitability have been found to be feedstock cost, product selling price and throughput. Given the economic conditions of late 1985, refuse gasification for the production of producer gas was found to be viable at throughputs of about 2.5 tonnes/h dry basis and above, in the metropolitan counties of the United Kingdom. At this throughput and above, the largest element of product gas cost is the feedstock cost, the cost element which is most variable.
5
Alonso, Lozano Alvaro. "Coal gasification in entrained flow gasifiers simulation & comparison". Thesis, Högskolan i Gävle, Avdelningen för bygg- energi- och miljöteknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-12726.
Testo completo
6
Mirmoshtaghi, Guilnaz. "Biomass gasification in fluidized bed gasifiers : Modeling and simulation". Doctoral thesis, Mälardalens högskola, Framtidens energi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-33426.
Testo completoAbstract (sommario):
Using woody biomass as a resource for production of biofuel, heat and power through gasification has been studied for years. In order to reduce the cost of operating and to design the full-scale gasification plant developing a general model to be applicable for different ranges of input data with acceptable level of accuracy, is needed. In order to develop such model for the gasifier, as the main component in the process, three major models have been studied in this thesis; theoretical model (Equilibrium model), semi-empirical model (modified equilibrium model, kinetic combined with hydrodynamic model) and empirical model (statistical model). Equilibrium model (EM), shows low accuracy in predicting the content ofmajor components in product gas especially CH4 and CO. Therefore to improve the accuracy of prediction modification of EM is needed. Analyzing the semi-empirical approaches show that although the accuracy of EM can be improved, the generality of the modified models are still low. Therefore two new modified models have been developed. The first model is based on including data from wider range of operating condition to develop the empirical equation. The second model is based on combining QET and reaction kinetics for char gasification approaches. The first model decreases the overall error from 44% to 31% while the overall error of second model is decreased from 36% to 8%. Other semi-empirical model for fluidized bed gasifiers which is not equilibrium-based is developed by combining reaction kinetics with hydrodynamic equations. Investigating different hydrodynamic models show that combining two-phase-structure model with reaction kinetics for bubbling fluidized bed gasifiers improves the accuracy of the kinetic-only model. The third type of approaches, investigated in this thesis, towards developing a general model is the empirical model. This model has been developed based on Partial least square (PLS) approach. The PLS-R model show high level of accuracy within the specific range of empirical data used for developing the model. Further analysis on the experimental dataset by PLS-R model show that equivalence ratio (ER) is the operating parameter with the most significant impact on the performance of fluidized bed gasifiers. Optimizing the operation of fluidized bed gasifiers based on this model shows that high gas quality (high volume fraction of H2, CO and CH4 and low volume fraction of CO2), high carbon conversion and low tar yield is achieved when ER≈0.3, Steam to Biomass ratio≈0.7, moisture content≈9% and particle size≈3mm and olivine is the bed material.
7
Puig, Arnavat Maria. "Performance modelling and validation of biomass gasifiers for trigeneration plants". Doctoral thesis, Universitat Rovira i Virgili, 2011. http://hdl.handle.net/10803/51880.
Testo completoAbstract (sommario):
Esta tesis desarrolla un modelo sencillo pero riguroso de plantas de trigeneración con gasificación de biomasa para su simulación, diseño y evaluación preliminar. Incluye una revisión y estudio de diferentes modelos propuestos para el proceso de gasificación de biomasa.Desarrolla un modelo modificado de equilibrio termodinámico para su aplicación a procesos reales que no alcanzan el equilibrio así comodos modelos de redes neuronales basados en datos experimentales publicados: uno para gasificadores BFB y otro para gasificadores CFB. Ambos modelos, ofrecen la oportunidad de evaluar la influencia de las variaciones de la biomasa y las condiciones de operación en la calidad del gas producido. Estos modelos se integran en el modelo de la planta de trigeneración con gasificación de biomasa de pequeña-mediana escala y se proponen tres configuraciones para la generación de electricidad, frío y calor. Estas configuraciones se aplican a la planta de poligeneración ST-2 prevista en Cerdanyola del Vallés.This thesis develops a simple but rigorous model for simulation, design and preliminary evaluation of trigeneration plants based on biomass gasification. It includes a review and study of various models proposed for the biomass gasification process and different plant configurations. A modified thermodynamic equilibrium model is developed for application to real processes that do not reach equilibrium. In addition, two artificial neural network models, based on experimental published data, are also developed: one for BFB gasifiers and one for CFB gasifiers. Both models offer the opportunity to evaluate the influence of variations of biomass and operating conditions on the quality of gas produced. The different models are integrated into the global model of a small-medium scale biomass gasification trigeneration plant proposing three different configurations for the generation of electricity, heat and cold. These configurations are applied to a case study of the ST-2 polygeneration plant foreseen inCerdanyola del Valles.
8
Gustafsson, Eva. "Characterization of particulate matter from atmospheric fluidized bed biomass gasifiers". Doctoral thesis, Linnéuniversitetet, Institutionen för teknik, TEK, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-11473.
Testo completoAbstract (sommario):
Through biomass gasification, biomass can be converted at high temperature to a product gas rich in carbon monoxide, hydrogen, and methane. After cleaning and upgrading, the product gas can be converted to biofuels such as hydrogen; methanol; dimethyl ether; and synthetic diesel, gasoline, and natural gas. Particulate matter (PM) is formed as a contaminant in the gasification process, and the aim of this work was to develop and apply a method for sampling and characterization of PM in the hot product gas. A particle measurement system consisting of a dilution probe combined in series with a bed of granular activated carbon for tar adsorption was developed, with the aim of extracting a sample of the hot product gas without changing the size distribution and composition of the PM. The mass size distribution and concentration, as well as the morphology and elementary composition, of PM in the size range 10 nm to 10 µm in the product gas from a bubbling fluidized bed (BFB) gasifier, a circulating fluidized bed (CFB) gasifier and an indirect BFB gasifier using various types of biomass as fuel were determined. All gasifiers and fuels displayed a bimodal particle mass size distribution with a fine mode in the <0.5 µm size range and a coarse mode in the >0.5 µm size range. Compared with the mass concentration of the coarse mode the mass concentration of the fine mode was low from all gasifiers. The evaluation of the results for the fine-mode PM was complicated by condensing potassium chloride for the CFB gasifier when using miscanthus as fuel and by condensing tars for the indirect BFB gasifier when using wood C as fuel. The mass concentration of the coarse-mode PM was higher from the CFB gasifier than from the two BFB gasifiers. The coarse-mode PM from the BFB gasifier when using wood A as fuel was dominated by char. In the CFB gasifier the coarse-mode PM was mainly ash and bed material when using all fuels. The coarse-mode PM from the indirect BFB gasifier when using wood C as fuel was mainly ash.
9
Silaen, Armin. "Comprehensive Modeling and Numerical Investigation of Entrained-Flow Coal Gasifiers". ScholarWorks@UNO, 2010. http://scholarworks.uno.edu/td/1148.
Testo completoAbstract (sommario):
Numerical simulations of coal gasification process inside a generic 2-stage entrainedflow gasifier are carried out using the commercial CFD solver ANSYS/FLUENT. The 3-D Navier-Stokes equations and eight species transport equations are solved with three heterogeneous global reactions, three homogeneous reactions, and one thermal cracking equation of volatiles. Finite rates are used for the heterogeneous solid-gas reactions. Both finite rate and eddy-breakup combustion models are calculated for each homogeneous gas-gas reaction, and the smaller of the two rates is used. Lagrangian-Eulerian method is employed. The Eulerian method calculates the continuous phase while the Lagrangian method tracks each coal particle. Fundamental study is carried out to investigate effects of five turbulence models (standard k-ε, k-ω, RSM, k-ω SST, and k-ε RNG) and four devolatilization models (Kobayashi, single rate, constant rate, and CPD) on gasification simulation. A study is also conducted to investigate the effects of different operation parameters on gasification process including coal mixture (dry vs. slurry), oxidant (oxygen-blown vs. air-blown), and different coal distributions between two stages. Finite-rate model and instantaneous gasification model are compared. It is revealed that the instantaneous gasification approach can provide an overall evaluation of relative changes of gasifier performance in terms of temperature, heating value, and gasification efficiency corresponding to parametric variations, but not adequately capture the local gasification process predicted by the finite rate model in most part of the gasifier. Simulations are performed to help with design modifications of a small industrial demonstration entrained-flow gasifier. It is discovered that the benefit of opening the slag tap on the quench-type gasifier wider by allowing slag to move successfully without clogging is compromised by increased heat losses, reduced gasification performance, downgraded syngas heating value, and increased unburned volatiles. The investigation of heat transfer on fuel injectors shows that blunt tip fuel injector is less likely to fail compared to conical tip fuel injector because the maximum high temperature on the injector is scattered. Two concentric fuel/oxidant injections provide better fuel-oxidant mixing and higher syngas heating value than four separate fuel and oxidant injections.
10
Pallay, Krista Joy. "Surface Modifications to Mitigate Refractory Degradation in High-Temperature Black Liquor Gasifiers". Thesis, Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10488.
Testo completoAbstract (sommario):
Ceria (CeO2), chromia (Cr2O3), yttria-stabilized zirconia (Y2O3-ZrO2), and sodium cerium oxide (Na2CeO3) were used as barrier coatings on Ufala, an alumina-based ceramic refractory, to determine if they were effective at increasing the life of the refractory in a high-temperature black liquor gasification environment. The ceria, chromia, and yttria-stabilized zirconia coatings were applied at atmospheric pressure using a coating applicator at the Institute of Paper Science and Technology at the Georgia Institute of Technology. The sodium cerium oxide coatings in addition to the three other coating types were applied under atmospheric pressure at C3 International Technologies in Alpharetta, GA. The coated refractory, as well as a set of uncoated refractory used for baseline analysis, were tested using molten synthetic smelt at 1000C for 36 hours. Uncoated refractory samples were also tested for 12, 72, 120, and 168 hours in order to make a kinetic reaction rate determination. The refractory were analyzed using gravimetric and dimensional analysis, X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy to determine the severity of the physical changes that occurred after exposure to molten smelt. The data gathered from these experiments were not able to conclude that barrier coatings are sufficient to impede corrosion of the Ufala refractory material in molten smelt.
11
Kieffer, Benoit. "Potential market for small-scale gasifiers in rural areas of developing countries". Thesis, KTH, Kraft- och värmeteknologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-145649.
Testo completoAbstract (sommario):
This thesis report assesses the potential market for small-scale gasifiers in rural areas of developing countries and regions. Biomass is already widely used in these areas for energetic purpose, giving gasification an interesting niche market for remote electricity production. Success factors include a high reliability, an efficient biomass supply chain and sufficient local electricity needs. Suitable fuel for a gasifier must be available at low cost, which could be wood harvested locally or agricultural residues such as rice husks or nut shells. A good potential for gasifiers fueled by wood has been identified in Eastern Africa, based on FAO's wood supply-demand models. South-East Asia and South America produce a lot of agricultural residues suitable for gasification. However, the electrification rate in South America is already high, which reduces considerably the interest for small-scale decentralized electricity production. Taking into account all these parameters, the most promising countries are Nigeria, India, Myanmar and Indonesia. Thailand, Cambodia and the Philippines also offer opportunities in the rice and sugar industries, while the wood industry in Cameroon shall deserve a deeper investigation.
12
Souza-Santos, Marcio Luiz de. "Modelling and simulation of fluidized-bed boilers and gasifiers for carbonaceous solids". Thesis, University of Sheffield, 1987. http://etheses.whiterose.ac.uk/1857/.
Testo completoAbstract (sommario):
SUMMARY A comprehensive computer simulation program that can deal with a wide range of different operating conditions in fluidized bed combustion and gasification has been developed. It includes the possibility of simulating operations with various types of coal, charcoal or wood and can predict the behaviour of a real unit by giving several important performance parameters, such as: (a) Emulsion and bubble gas composition profiles throughout the bed height. The components included are: CO2 , CO, 02, N 2 , H2 0, H2 , CH4 , SO2 , NO, C2 H 6 , H2 S, NH3 and Tar. (b) Gas phase composition throughout the freeboard height. (c) Solid compositions of the coal (or any other carbonaceous material), limestone and inert in the bed and throughout the freeboard. The considered components are: C, H, 0, N, S, ash, volatiles, moisture in the coal, CaCO3, CaO, CaSO4 , moisture in the limestone, Si0 2 , and moisture in the inert. (d) Temperature profiles of all phases throughout the bed and the freeboard. (e) Solid particle size distributions in the bed and in the freeboard sections. The considered effects are: elutriation, entrainment, attrition and recycling in all the three possible types of solid phases present; (f) Heat transfered to water/steam inside the tubes, steam production and tube surface temperatures in the case of boiler simulation.
13
Xu, Qixiang. "Investigation of Co-Gasification Characteristics of Biomass and Coal in Fluidized Bed Gasifiers". Thesis, University of Canterbury. Chemical and Process, 2013. http://hdl.handle.net/10092/8399.
Testo completoAbstract (sommario):
This thesis presents research on the co-gasification characteristic of biomass and coal, and mathematical modelling of the co-gasification process in two main parts: i) experimental investigation and mathematical modelling of reaction kinetics of steam gasification of single char particles of pure coal, pure biomass, and blended coal and biomass; and ii) Experimental investigation and mathematical modelling of gasification characteristics of biomass, coal and their blends in pilot scale gasifiers. From the char reactivity study, the instinct difference in gasification characteristics of the two chars has been explained and reactivity of blended char can be predicted. In the pilot scale gasifier study, effects of blending ratio in feedstock and operating conditions on co-gasification of biomass and coal were investigated.
14
Göransson, Kristina. "Internal Tar/CH4 Reforming in Biomass Dual Fluidised Bed Gasifiers towards Fuel Synthesis". Doctoral thesis, Mittuniversitetet, Avdelningen för kemiteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-22984.
Testo completoAbstract (sommario):
Production of high-quality syngas from biomass gasification in a dual fluidised bed gasifier (DFBG) has made a significant progress in R&D and Technology demonstration. An S&M scale bio-automotive fuel plant close to the feedstock resources is preferable as biomass feedstock is widely sparse and has relatively low density, low heating value and high moisture content. This requires simple, reliable and cost-effective production of clean and good syngas. Indirect DFBGs, with steam as the gasification agent, produce a syngas of high content H2 and CO with 12-20 MJ/mn3 heating value. The Mid Sweden University (MIUN) gasifier, built for research on synthetic fuel production, is a dual fluidised bed gasifier. Reforming of tars and CH4 (except for methanation application) in the syngas is a major challenge for commercialization of biomass fluidised-bed gasification technology towards automotive fuel production. A good syngas from DFBGs can be obtained by optimised design and operation of the gasifier, by the use of active catalytic bed material and internal reforming. This thesis presents a series of experimental tests with different operation parameters, reforming of tar and CH4 with catalytic bed material and reforming of tar and CH4 with catalytic internal reformer. The first test was carried out to evaluate the optimal operation and performance of the MIUN gasifier. The test provides basic information for temperature control in the combustor and the gasifier by the bed material circulation rate. After proven operation and performance of the MIUN gasifier, an experimental study on in-bed material catalytic reforming of tar/CH4 is performed to evaluate the catalytic effects of the olivine and Fe-impregnated olivine (10%wtFe/olivine Catalyst) bed materials, with reference to non-catalytic silica sand operated in the mode of dual fluidised beds (DFB). A comparative experimental test is then carried out with the same operation condition and bed-materials but when the gasifier was operated in the mode of single bubbling fluidised bed (BFB). The behaviour of catalytic and non-catalytic bed materials differs when they are used in the DFB and the BFB. Fe/olivine and olivine in the BFB mode give lower tar and CH4 content together with higher H2+CO concentration, and higher H2/CO ratio, compared to DFB mode. It is hard to show a clear advantage of Fe/olivine over olivine regarding tar/CH4 catalytic reforming. In order to significantly reduce the tar/CH4 contents, an internal reformer, referred to as the FreeRef reformer, is developed for in-situ catalytic reforming of tar and CH4 using Ni-catalyst in an environment of good gas-solids contact at high temperature. A study on the internal reformer filled with and without Ni-catalytic pellets was carried out by evaluation of the syngas composition and tar/CH4 content. It can be concluded that the reformer with Ni-catalytic pellets clearly gives a higher H2 content together with lower CH4 and tar contents in the syngas than the reformer without Ni-catalytic pellets. The gravimetric tar content decreases from 25 g/m3 down to 5 g/m3 and the CH4 content from 11% down below 6% in the syngas. The MIUN gasifier has a unique design suitable for in-bed tar/CH4 catalytic reforming and continuously internal regeneration of the reactive bed material. The novel design in the MIUN gasifier increases the gasification efficiency, suppresses the tar generation and upgrades the syngas composition.Gasification-based Biorefinery for Mechanical Pulp Mills
15
Kuhn, John N. "Investigation of catalytic phenomena for solid oxide fuel cells and tar removal in biomass gasifiers". Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1186755244.
Testo completo
16
Brooks, Amelia (Amelia Samek). "Modeling of char oxidation in fluidized bed biomass gasifiers : effects of transport and chemical kinetics". Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98959.
Testo completoAbstract (sommario):
Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (page 36).
Technologies for the conversion of biomass to liquid fuels are important to develop because the demand for liquid fuels remains unchanged even with the necessity of limiting dependence on fossil fuels. Fluidized Bed Biomass Gasification (FBBG) is one such technology that can perform the initial step of converting raw biomass into syngas as an intermediate to liquid fuels. The char that is left in the reactor after devolatilization can be oxidized in order to maximize the amount of biomass carbon that is converted to gaseous carbon and generate heat to drive endothermic gasification reactions. This paper examines the rate of each of the three processes that occur during char conversion (external diffusion, chemical reactions, and intraparticle diffusion) to determine which process limits the rate of the reaction under a range of conditions. It was determined that at most FBBG operating points, the rate of char conversion will be limited by the rate of diffusion of oxygen through the particle's boundary layer and through its pores. Only at low reactor temperatures and small particle diameters will the reaction rate be purely kinetically limited. An overall rate expression accounting for all three processes has been formulated which can be implemented in more detailed reactor models.
by Amelia Brooks.
S.B.
17
Kuhn, John. "Investigation of catalytic phenomena for solid oxide fuel cells and tar removal in biomass gasifiers". The Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=osu1186755244.
Testo completo
18
Gonzalez, Anselmo Dueñas 1968. "Caracterização e análise comparativa de cinzas provenientes da queima de biomassa". [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265872.
Testo completoAbstract (sommario):
Orientador: Caio Glauco SánchezDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: O presente trabalho apresenta o desenvolvimento de um processo de caraterização das cinzas das biomassas bagaço de cana-de-açúcar, eucalipto e capim elefante após sua queima quando utilizadas para geração de energia alternativa. É, então, analisada a influência de parâmetros físico-químicos na qualidade final das cinzas. O parâmetro químico avaliado foi a interpretação da composição elementar das cinzas estudadas por análises de Espectrometria de Fluorescência de Raios-X e Cromatografia de Íons e por Análise Química por, objetivando a caracterização e reutilização desses resíduos. As amostras de cinzas de biomassas estudadas neste trabalho, foram analisadas quanto à presença dos elementos Cloro (Cl-), Alumínio (em Al2O3), Cálcio (em CaO), Ferro (em Fe2O3), Fósforo (em P2O5), Magnésio (em MgO), Manganês (em MnO), Potássio (em K20), Sódio (em Na2O) e Silício (em SiO2), e foram caracterizadas conforme os percentuais em massa dos elementos presentes. Os resultados obtidos mostraram a possibilidade de reutilização adequada de cinzas das biomassas em função da alteração das propriedades químicas do solo, por ocorrência de elevação dos níveis de pH, Cálcio (Ca), Fósforo (P), redução dos teores de Alumínio (Al) trocável e melhoria substancial da capacidade de agregação das partículas e fertilização do solo. Também foram associadas as influências dos elementos presentes nas cinzas como alternativa viável na composição do cimento Portland, em especial, o Silício (em SiO2). As cinzas das biomassas possuem nutrientes que estão na forma solúvel e são libertados ao longo do tempo devido à sua decomposição contínua e também pela solubilidade dos compostos químicos, o que, consequentemente, torna os nutrientes menos suscetíveis à lixiviação
Abstract: This paper presents the development of a process of characterization of the ashes of biomass bagasse from sugar cane, eucalyptus and elephant grass after its burning when used for alternative energy generation. It then analyzed the influence of physicochemical parameters on the final quality of the ash. The chemical parameter evaluated was the interpretation of the elemental composition of the ash studied by analysis Fluorescence Spectrometry X-Ray and Ion Chromatography and Chemical Analysis, aiming at characterization and reuse of the waste. The ashes from biomass samples studied in this work were analyzed for the presence of chlorine (Cl-), aluminum (as Al2O3), calcium (as CaO), iron (as Fe2O3), phosphorus (as P2O5), Magnesium elements (as MgO), manganese (as MnO), Potassium (as K20) Sodium (as Na2O) and silicon (as SiO2), and were characterized as the weight percentage of the elements present. The results showed the possibility of proper reuse of ashes of biomass due to changes in chemical properties of the soil, by the occurrence of elevated levels of pH, calcium (Ca), phosphorus (P), reduced levels of aluminum (l) the significant improvement exchangeable capacity of aggregation of particles and soil fertilization. Were also associated with the influences of the elements present in the ash as a viable alternative in the composition of the Portland cement, in particular, silicon (as SiO2). The ash of the biomass have nutrients that are in soluble form and are released over time due to its continuous decomposition and also by the solubility of the chemical compounds, which consequently makes them less susceptible to leaching nutrients
Mestrado
Termica e Fluidos
Mestre em Engenharia Mecânica
19
Stoesser, Philipp [Verfasser]. "Investigation of solid-phase processes during the conversion of biogenic slurry in entrained-flow gasifiers / Philipp Stoesser". München : Verlag Dr. Hut, 2020. http://d-nb.info/1219475548/34.
Testo completo
20
Rutherford, John Peter. "Heat and Power Applications of Advanced Biomass Gasifiers in New Zealand's Wood Industry A Chemical Equilibrium Model and Economic Feasibility Assessment". Thesis, University of Canterbury. Chemical and Process Engineering, 2006. http://hdl.handle.net/10092/1142.
Testo completoAbstract (sommario):
The Biomass Integrated Gasification Application Systems (BIGAS) consortium is a research group whose focus is on developing modern biomass gasification technology for New Zealand's wood industry. This thesis is undertaken under objective four of the BIGAS consortium, whose goal is to develop modelling tools for aiding in the design of pilot-scale gasification plant and for assessing the economic feasibility of gasification energy plant. This thesis presents a chemical equilibrium-based gasification model and an economic feasibility assessment of gasification energy plant. Chemical equilibrium is proven to accurately predict product gas composition for large scale, greater than one megawatt thermal, updraft gasification. However, chemical equilibrium does not perform as well for small scale, 100 to 150 kilowatt thermal, Fast Internally Circulating Fluidised Bed (FICFB) gasification. Chemical equilibrium provides a number of insights on how altering gasification parameters will affect the composition of the product gas and will provide a useful tool in the design of pilot-scale plant. The economic model gives a basis for judging the optimal process and the overall appeal of integrating biomass gasification-based heat and power plants into New Zealand's MDF industry. The model is what Gerrard (2000) defines as a 'study estimate' model which has a probable range of accuracy of ±20% to ±30%. The modelling results show that gasification-gas engine plants are economically appealing when sized to meet the internal electricity demands of an MDF plant. However, biomass gasification combined cycle plants (BIGCC) and gasificationgas turbine plants are proven to be uneconomic in the New Zealand context.
21
Van, Dyk Johannes Chrisstoffel. "Manipulation of gasification coal feed in order to increase the ash fusion temperature of the coal to operate the gasifiers at higher temperatures / Johannes Chrisstoffel van Dyk". Thesis, North-West University, 2006. http://hdl.handle.net/10394/1331.
Testo completoAbstract (sommario):
Coal is a crucial feedstock for South Africa's unique synfuels and petrochemicals industry and used by Sasol as a feedstock to produce synthesis gas via the Sasol-Lurgi Fixed Bed Dry Bottom (FBDB) gasification process. The ash fusion temperature (AFT) gives detail information on the suitability of a coal source for gasification purposes, and specifically to the extent ash agglomeration or clinkering is likely to occur within the gasifier. Ash clinkering inside the gasifier can cause channel burning and unstable operation.
Sasol-Lurgi FBDB gasifiers are currently operated with the philosophy of adding an excess of steam to the process to control the H2/CO ratio of the syngas produced, but indirectly also to control the maximum gasifier temperature below the AFT of the coal. An opportunity exists to increase the AFT of the coal fed to the gasifiers by adding AFT increasing minerals to the coal blend before it is fed into the gasification process. For the aim of this study a typical Highveld Nr. 4 coal seam was investigated, as being used by the gasification operations in Secunda.
In the drying and devolatilization zone no slag formation in the coal was observed. Based on HT-XRD analysis the predominant phases in the untreated coal sample were quartz, muscovite, calcite, dolomite. hematite. anhydrite, rutile and kaolinite. Kaolinite started to decompose to metakaolinite at ±450°C with the formation of amongst others mullite at a temperature of 850°C to 1000°C. Mullite formation can also take place if free Al2O3 is present in the coal that can react with free SiO2. However, free Al2O3 is normally not present in coal and the presence of the aluminasilicate (Al2SiO5) is formed as an intermediate phase due to the decomposition of kaolinite. From 500°C to 900°C, the carbonates, calcite and dolomite, started to decompose with the formation of lime and
periclase. The feldspar (CaAl2Si2O8) observed, formed as a reaction product between the SiO2, Al2O3 and Ca-containing species present in the coal.
In the gasification zone slag-liquid formed at a temperature from 1000°C. The formation of anhydrite (CaSO4) took place after the formation of calcite. At 1000°C anorthite, initially present as feldspar (CaAl2Si2O8) and gehlenite (Ca2Al2SiO7) became stable, due to partial melting of the low AFT mineral phases. Anorthite and gehlenite were formed as products from anhydrite, alumina and silica at temperatures around 900°C to 1100°C. Mullite decomposed at temperatures >1100°C, while quartz and anorthite were observed up to 1350°C. Above 1350°C the whole mineral phase assemblage in the coal sample was molten. When comparing the base case sample with the Al2O3-manipulated sample, it was clear that the mullite is one mineral that showed a significant difference in formation and mechanistic behaviours.
In the combustion zone the decrease in the slag-liquid content confirmed the cooling and actual mineral formation and crystallization within the gasifier combustion zone. The representative coal ash, as it was produced after gasification, showed evidence of crystallization from the melt phase and formed due to the interaction of specific mineral species to produce a molten phase that had the correct chemistry to crystallize again.
Mullite formation can also take place when free Al2O3 in the coal is available that can react with free SiO2, also present in the coal. With the addition of y-Al2O3 the free SiO2 in the coal can react with the y-Al2O3 to form mullite (Al6O5(SiO4)2) directly. The Al2O3 in the reactive form acts as a network former where SiO2 can be reacted on, to form mullite. The main conclusion of the addition of y-Al2O3 to the blend is that the slag-liquid content decreased with addition, only when the temperature was greater than 1000oC, which is of importance in Me operating region where the proposed higher gasifier temperature of more than 1250°C, is aimed for.
Another observation from the AFT results was that the AFT was definitely non-additive (not a linear weighted calculated average) and not the weighted average AFT as was expected for the other coal properties such as the ash content, for example. The ash slagging behaviour is a non-additive property of individual coal sources in the blend and therefore difficult to predict. Viscosity modelling can be another tool for predicting slag mineral behaviour and used as a predicting tool, as has been done in this study. A higher viscosity for all relative density fractions were observed for all temperature ranges in comparison with the results obtained from the AFT analysis.
In general it can be concluded that the unique opportunity that exists to increase the AFT, was tested, proven and mechanistically outlined in this study on the coal source fed to the Sasol-Lurgi FBDB gasifiers. The AFT can be increased to > 1350°C by adding AFT increasing minerals or species, for example Al2O3 or other mineral species, to the coal blend before it is fed into the gasification process. By increasing the AFT, the direct effect will be that steam consumption can be decreased, which in tum will improve carbon utilization.Thesis (M. Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2006
22
Visagie, Johannes Petrus. "Generic gasifier modelling : evaluating model by gasifier type". Diss., University of Pretoria, 2008. http://hdl.handle.net/2263/26000.
Testo completoAbstract (sommario):
There are many different types of gasifiers used for commercial or research purposes. These gasifier varieties differ in a number of ways, such as the direction of material flow or the physical chemical contact between the different species. These differences affect the modelling procedure and philosophy required to describe the gasification processes accurately. Honeywell wishes to incorporate a generic gasifier model into their UNISIM DESIGN engine to simulate gasifiers accurately and calculate certain properties. Such a model does however not yet exist. Presented in this document is a summary of the similarities and mutual properties among the different coal gasifiers, which allow for certain generic modelling procedures to be followed. The paper also highlights the discrepancies among these gasifiers and the areas where different modelling approaches should be followed. Apart from the specific gasifier characteristics, the phenomena of reaction kinetics, heat transfer and mass transfer were also investigated to ascertain their significance on gasifiers and specifically gasifier modelling. By following the guidelines provided in this paper, it should be possible to develop a generic gasifier model in any modelling environment.Dissertation (MEng)--University of Pretoria, 2008.
Chemical Engineering
unrestricted
23
Visagie, J. P. "Generic gasifier modelling evaluating model by gasifier type /". Pretoria : [s.n.], 2009. http://upetd.up.ac.za/thesis/available/etd-07022009-133535.
Testo completo
24
Ardila, Yurany Camacho 1985. "Gaseificação da biomassa para a produção de gás de síntese e posterior fermentação para bioetanol : modelagem e simulação do processo". [s.n.], 2015. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266052.
Testo completoAbstract (sommario):
Orientadores: Maria Regina Wolf Maciel, Betânia Hoss LunelliTese (doutorado) ¿ Universidade Estadual de Campinas, Faculdade de Engenharia Química
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Resumo: A produção de biocombustíveis a partir da biomassa apresenta-se como uma alternativa para suprir as limitadas reservas de petróleo. A biomassa, atualmente, está sendo usada para diferentes processos termoquímicos, entre os quais a gaseificação é o de maior destaque. A gaseificação produz gás de síntese que é uma mistura, principalmente, de CO, H2 e CO2. Este gás serve para produzir energia, diferentes produtos químicos e biocombustíveis, como por exemplo, o bioetanol. A partir do gás de síntese, a produção de bioetanol pode ser realizada usando catalisadores químicos ou biocatalisadores, sendo este último processo conhecido como fermentação do gás de síntese. Para o processo integrado de gaseificação da biomassa e posterior fermentação para produção de bioetanol, as informações na literatura são escassas, o que dificulta avaliar a viabilidade desta nova tecnologia, em termos de condições operacionais. O uso de modelos matemáticos e sua simulação computacional podem auxiliar neste estudo. A literatura dispõe de vários estudos envolvendo simulações computacionais aplicadas à gaseificação de diferentes biomassas. Porém, poucos abordam a caracterização real do processo e as propriedades da biomassa utilizada, considerando apenas as propriedades para o carvão mineral, o que acaba gerando divergência nos resultados. Além disso, a maioria fundamenta suas simulações em modelos simples com base na caracterização elementar-imediata, que acaba limitando o desenvolvimento de plantas virtuais, que são baseadas na análise composicional da biomassa quando focadas na produção de bioetanol como etapa final ou como integração do processo. Assim, este trabalho tem como objetivos estudar o processo completo de gaseificação e realizar um estudo preliminar da fermentação do gás de síntese, mediante simulações computacionais, para definir as melhores condições e variáveis que afetam o processo global quando o bagaço de cana-de-açúcar é utilizado como matéria-prima. As simulações foram desenvolvidas utilizando o simulador comercial Aspen Plus¿ e os resultados validados com dados experimentais da literatura e dados obtidos nos Laboratórios LDPS/LOPCA/BIOEN/FEQ/UNICAMP. Para a completa simulação do processo, várias etapas foram estudadas e divididas para melhor entendimento. Foram desenvolvidos modelos matemáticos para predizer propriedades necessárias para o desenvolvimento de processos termoquímicos. Simulações baseadas nas análises elementar-imediata e composicional da biomassa foram realizadas para definir a decomposição inicial da biomassa, demonstrando os diferentes rendimentos e produtos que são gerados e que são a base da etapa inicial da gaseificação. Simulações completas da gaseificação foram desenvolvidas para estudar a gaseificação em diferentes tipos de reatores. A influência das condições de operação na gaseificação como temperatura, razão de equivalência (ER), injeção de vapor e temperatura do pré-aquecedor do ar no desempenho do gaseificador foram avaliadas. Com as condições operacionais da gaseificação definidas foi proposta uma simulação para representar a fermentação do gás de síntese. A partir dos resultados obtidos foi constatado que a composição do gás de síntese é alterada pelo aumento do ER e pela injeção de vapor no processo, e diferentes concentrações de bioetanol são obtidas quando a pressão de entrada do gás de síntese é alterada
Abstract: The production of biofuels from biomass is presented as an alternative to save the limited oil reserves. Currently, biomass is being used for different thermochemical processes, including gasification which is the most prominent. Gasification produces synthesis gas which is a mixture mainly of CO, H2 and CO2. This gas is used to produce energy, several chemicals and biofuels, such as ethanol. The ethanol from synthesis gas may be produced using chemical catalysts or biocatalysts, this latter process is known as fermentation of syngas. The information in the literature is scarce for the integrated gasification of biomass and subsequent fermentation to produce ethanol, making it difficult to see the feasibility of this new technology, in terms of operating conditions. The use of mathematical models and their computer simulation can help this study. Typically, numerous studies involving computer simulations, applied to different biomass gasification, are found in the literature. However, few of them approach the real characterization of process and properties for used biomass, considering only the properties for coal, which ends up generating divergence in the results. Moreover, most of the simulations are grounded on simple models based on proximate-ultimate characteristics, which end up limiting the development of virtual plants, which are based on biomass compositional analysis when focused on the production of ethanol as the final step or as integration process. Thus, the aims of this work are to study the complete gasification process and to carry out a preliminary study of synthesis gas fermentation, through computer simulations, in order to define the best conditions and variables that affect this global process when sugarcane bagasse is used as raw material. The simulations were developed using Aspen Plus ¿ simulator and the results validated with experimental data from literature and data obtained in the laboratories LDPS / LOPCA / BIOEN / FEQ / UNICAMP. For the full simulation of the process, several steps were studied and divided for a better understanding. Mathematical models were developed to predict properties required for the development of thermochemical processes. Simulations based on biomass analysis as proximate-ultimate and compositional were done to define the initial decomposition of biomass, demonstrating the different yields and products that are generated and which are the basis of the initial stage of the gasification. Complete simulations of gasification were carried out to study different types of gasification reactors. The influence of operating conditions at gasification performance was investigated; variables such as temperature, equivalence ratio (ER), steam injection and preheater temperature were evaluated. With the set conditions of gasification was proposed a simulation to represent the fermentation of syngas. It was demonstrated that the synthesis gas composition is changed when increased the ER and steam injection; and different ethanol concentrations are obtained when the input pressure of the synthesis gas is changed
Doutorado
Desenvolvimento de Processos Químicos
Doutora em Engenharia Quimica
25
James, Rivas Arthur Mc Carty. "The effect of biomass, operating conditions, and gasifier design on the performance of an updraft biomass gasifier". Thesis, Kansas State University, 2012. http://hdl.handle.net/2097/13794.
Testo completoAbstract (sommario):
Master of ScienceDepartment of Biological and Agricultural Engineering
Wenqiao Yuan
Gasification is an efficient way to produce energy from biomass, which has significant positive impacts on the environment, domestic economy, national energy security, and the society in general. In this study, a lab-scale updraft biomass gasifier was designed, built, and instrumented for stable gasification using low-bulk density biomass. Related accessories, such as a biomass feeder, inlet air temperature controller, air injection nozzle, and tar cracking system, were also developed to enhance gasifier performance. The effect of operation parameters on gasifier performance was studied. Two operational parameters, including air flow rate and feed-air temperature, were studied on three sources of biomass: prairie hay, sorghum biomass, and wood chips. Results showed that higher air flow rate increased tar contents in syngas for all three types. It was also found that different biomasses gave significantly different tar contents, in the order of wood chips>sorghum biomass>prairie hay. Feed-air temperature did not have a significant effect on tar content in syngas except for prairie hay, where higher feed air temperature reduced tar. A statistical model was implemented to study differences on syngas composition. Results showed that different biomasses produced syngas with different high heating value, e.g., wood chips > prairie hay > sorghum biomass. CO composition also showed differences by feed air temperature and biomass, e.g. prairie hay>wood chips>sorghum biomass, but H[subscript]2 did not show significant differences by either biomass type or operating conditions. Moreover, because of the downstream problems caused by tars in syngas such as tar condensation in pipelines, blockage and machinery collapse, an in-situ tar cracking system was developed to remove tars in syngas. The tar cracking device was built in the middle of the gasifier’s combustion using gasification heat to drive the reactions. The in-situ system was found to be very effective in tar removal and syngas enhancement. The highest tar removal of 95% was achieved at 0.3s residence time and 10% nickel loading. This condition also gave the highest syngas HHV increment of 36% (7.33 MJ/m[superscript]3). The effect of gas residence time and Ni loading on tar removal and syngas composition was also studied. Gas residence of 0.2-0.3s and Ni loading of 10% were found appropriate in this study.
26
Fraser, Thomas. "Numerical modelling of an inverted cyclone gasifier". Thesis, Cardiff University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.407403.
Testo completo
27
Salman, Hassan. "Biomass feeding system for a cyclone gasifier". Licentiate thesis, Luleå tekniska universitet, 1999. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-25666.
Testo completo
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Gentile, Maria. "Alkali attack of coal gasifier refractory lining". Thesis, Virginia Tech, 1987. http://hdl.handle.net/10919/45668.
Testo completoAbstract (sommario):
An experimental test system was designed to simulate the operating conditions found in nonslagging coal gasifiers. The reaction products that form when refractory linings in coal gasifiers are exposed to alkali impurities (sodium or potassium) were experimentally determined. Analysis of selected physical and chemical properties of the reaction products, which typically form between the alkali and the refractory will lead to a better understanding of the mechanisms behind refractory failures associated with alkali attack.
The reaction products sodium aluminate (Na₂O⋅Al₂O₃), N₂C₃A₅ (2Na₂O·3CaO·5A1₂O₃), nepheline (Na20â ¢Al203â ¢2SiO2), potassium aluminate, (K2Oâ ¢Al203), and kaliophilite (K2Oâ ¢Al203â ¢2Si02) were synthesized and their solubility in water and coefficients of linear thermal expansion were: measured. Of the compounds tested, the formation of potassium aluminate would be the most detrimental to the gasifier lining. The linear thermal expansion of potassium aluminate was 2.05% from room temperature to 800°C, which was twice as large as the other compounds. Potassium aluminate also possessed the highest solubility in water which was 8.893/L at 90°C.
Master of Science
29
Sun, Tawei. "Alkali attack of coal gasifier refractory linings". Thesis, Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/94471.
Testo completoAbstract (sommario):
Thermodynamic calculations are used to study the alkali reactions in coal gasifier atmospheres. The reactive alkali and sulfur species released from coal are first calculated at temperatures from 800 K to 1900 K and pressures from 1 atm to 100 atm. Four P-T diagrams are constructed for the stable alkali and/or alkali-sulfur species at differ-ent temperatures and pressures. Alkali vapors are generated by the reactions
Na₂CO₃(s) + 2C(s) = 2Na(g) + 3CO(g)
Na₂CO₃(s) + H₂O(g) + C(s) = 2NaOH(g) + 2CO(g)
or
K₂CO₃(s) + 2C(s) = 2K(g) + 3CO(g)
K₂CO₃(s) + H₂O(g) + C(s) = 2KOH(g) + 2CO(g)
The phases formed from alkali-cement, and alkali-sulfur-cement reaction are also predicted. For both 53% and 72% alumina cement, calcium aluminate (CaO•Al₂O₃) is decomposed by the reactions
CaO•Al₂O₃ + 2Na + 1/20₂ = Na₂O•Al₂O₃ + CaO
CaO•Al₂O₃ + 2K + 1/20₂ = K₂O•Al₂O₃ + CaO
or
CaO•Al₂O₃ + 2Na + l/2S₂ = Na₂0•Al₂O₃ + CaS
CaO•Al₂O₃ + 2K + 1/2S₂ = K₂•Al₂O₃ + CaSM.S.
30
Lee, Kyoung-Ho. "Alkali attack on coal gasifier refractory lining". Thesis, Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/80163.
Testo completoAbstract (sommario):
For a given coal gasification atmosphere, the reactions between fired alumina-chromia solid solution refractories and alkali (sodium and potassium) with and without sulfur at varying alkali concentrations were thermodynamically calculated using the SOLGASMIX-PV computer program and the results were experimentally confirmed. In addition, the kinetics of alkali diffusion into the refractory were experimentally determined as a function of time and temperature.
The results, both experimental and theoretical, show formation of alkali-aluminate (Na₂O⋅Al₂O₃, K₂O⋅Al₂O₃) and β-alumina (Na₂O⋅11Al₂O₃, K₂O⋅11A₂O₃) compounds with formation of several metastable alkali compounds in a coal gasification environment. Sulfur did not appear to affect the reaction products. Alkali distribution into the alumina-chrome refractory is rapid and the formation of the Na₂O⋅Al₂O/K₂O⋅Al₂O₃ compounds cause large volume expansion from the reaction surface which causes poor thermal shock resistance and eventual refractory failure. The hot face of an alumina-chrome refractory in service in an alkali environment will be prone to failure by alkali attack.Master of Science
31
Hoi, W. H. "Gasification of rubberwood in a downdraft gasifier". Thesis, Aston University, 1991. http://publications.aston.ac.uk/9798/.
Testo completoAbstract (sommario):
The objectives of this research were to investigate the perforamnce of a rubberwood gasifier and engine with electricity generation and to identify opportunities for the implementation of such a system in Malaysia. The experimental work included the design, fabrication and commissioning of a throated downdraft gasifier in Malaysia. The gasifier was subsequently used to investigate the effect of moisture content, dry wood capacity and particle size of rubberwood on gasifier performance. Additional experiments were also conducted to investigate the influence of two different nozzle numbers and two different throat diameters on tar cracking. A total of 101 runs were completed during the duration of the research. From the experimental data, the average mass balance was found to be 92.65%. The average energy balance over the gasifier to hot raw gas was 98.7%, to cold clean gas was 102.4% and over the complete system was 101.9%. The heat loss from the gasifier was estimated to range from 10-26% of the chemical energy of the feedstock. From the downstream operation, the heat loss was estimated to range from 17-37% of the chemical energy of rubberwood feedstock. The maximum throughput for stable operation was found to be 60-70% of the maximum dry wood capacity. The gasifier was found to have a maximum turndown ratio of 5:1. It is also postulated that the phenomenon of turndown of the gasifier is due to a `bubble theory' occurring at the gasification zone, and this hypothesis is explained. For stable power output, the working range of the engine was found to be 5-33.5 kWe. The thermal efficiency and diesel displacement of the engine was found to be 17-18% and 65-70% respectively. The research also showed that rubberwood gasification in Malaysia is feasible if the price of diesel is above MR35/l and the price of wood is below MR120/tonne.
32
Kandamby, Naminda Harisinghe. "Mathematical modelling of gasifier fuelled gas turbine combustors". Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267305.
Testo completo
33
Alauddin, Zainal Alimuddin Zainal. "Performance and characteristics of a biomass gasifier system". Thesis, Cardiff University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399202.
Testo completo
34
Rathbone, R. R. "Gasification and combustion in fluidised bed". Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233249.
Testo completo
35
Lu, You. "Computational Scheme Guided Design of a Hybrid Mild Gasifier". ScholarWorks@UNO, 2012. http://scholarworks.uno.edu/td/1526.
Testo completoAbstract (sommario):
A mild gasification method has been developed to provide an innovative clean coal technology. The objectives of this study are to (a) incorporate a fixed rate devolatilization model into the existing 2D multiphase reaction model, (b) expand the 2D model to 3D and (c) utilize the improved model to investigate the mild-gasification process and guide modification of the mild-gasifier design. The Eulerain-Eulerian method is employed to calculate both the primary phase (air) and secondary phase (coal particles). The improved 3D simulation model, incorporated with a devolatilization model, has been successfully developed and employed to determine the appropriate draft tube dimensions, entrained flow residence time, The simulations also help determine the appropriate operating fluidization velocity range to sustain the fluidized bed depth without depleting the chars or blowing the char away. The results are informative, but require future experimental data for verification.
36
Kasedde, Hillary. "Hazard and Safety Evaluation of Gasifier Installations in Uganda". Thesis, KTH, Energiteknik, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-194335.
Testo completo
37
Kusar, Henrik. "Catalytic combustion of gasified waste". Doctoral thesis, KTH, Chemical Engineering and Technology, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3600.
Testo completoAbstract (sommario):
This thesis concerns catalytic combustion for gas turbineapplication using a low heating-value (LHV) gas, derived fromgasified waste. The main research in catalytic combustionfocuses on methane as fuel, but an increasing interest isdirected towards catalytic combustion of LHV fuels. This thesisshows that it is possible to catalytically combust a LHV gasand to oxidize fuel-bound nitrogen (NH3) directly into N2without forming NOX. The first part of the thesis gives abackground to the system. It defines waste, shortly describesgasification and more thoroughly catalytic combustion.
The second part of the present thesis, paper I, concerns thedevelopment and testing of potential catalysts for catalyticcombustion of LHV gases. The objective of this work was toinvestigate the possibility to use a stable metal oxide insteadof noble metals as ignition catalyst and at the same timereduce the formation of NOX. In paper II pilot-scale tests werecarried out to prove the potential of catalytic combustionusing real gasified waste and to compare with the resultsobtained in laboratory scale using a synthetic gas simulatinggasified waste. In paper III, selective catalytic oxidation fordecreasing the NOX formation from fuel-bound nitrogen wasexamined using two different approaches: fuel-lean andfuel-rich conditions.
Finally, the last part of the thesis deals with deactivationof catalysts. The various deactivation processes which mayaffect high-temperature catalytic combustion are reviewed inpaper IV. In paper V the poisoning effect of low amounts ofsulfur was studied; various metal oxides as well as supportedpalladium and platinum catalysts were used as catalysts forcombustion of a synthetic gas.
In conclusion, with the results obtained in this thesis itwould be possible to compose a working catalytic system for gasturbine application using a LHV gas.
Keywords:Catalytic combustion; Gasified waste; LHVfuel; RDF; Biomass; Selective catalytic oxidation; NH3; NOX;Palladium; Platinum; Hexaaluminate; Garnet; Spinel;Deactivation; Sulfur; Poisoning
38
Kithinji, Jacob P. "Extraction and chromatography of supercritical fluids". Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329092.
Testo completo
39
Al-Farraji, Abbas. "Chemical engineering and reactor design of a fluidised bed gasifier". Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/104985/.
Testo completoAbstract (sommario):
The design, modelling and optimisation of biofuel thermochemical processes are mainly based on the knowledge of reliable chemical kinetics. The determination of reaction kinetics of biomass at high heating rate still highly depends on the extrapolation of results from kinetic data determined at a comparatively low heating rate. To provide more comprehensive kinetic data for gas-solid reactions under isothermal conditions, a thermogravimetric fluidized bed reactor (TGFBR) was designed. Using this novel fluidised bed, gravimetric measurements and high heating rate, the thermal conversion of biomass was investigated. Using a thermogravimetric analyser (TGA) as a fixed bed and the TGFBR as a fluidized bed, the pyrolysis kinetics of olive kernels was studied. The pyrolysis in the TGFBR was analysed using the isothermal kinetic approach and it was theorised that the pyrolysis decomposition reaction occurred by two mechansims. Dependent on the temperature, the resultant activation energy was 67.4 kJ/mole at < 500 °C and 60.8 kJ/mole at > 500 °C. For comparsion, the TGA gave a higher activation energy of 74.4 kJ/mole due to external particle diffusion. To study the impact of torrefaction on gasification performance, gasification experiments were performed on “as received olive kernels” (AROK) and “as received torrefied olive kernels” (ARTOK) in the TGFBR. The effect of equivalence ratio (ER) (0.15-0.35) and bed temperature (550-750°C) on gasification performance was investigated. Based on thermogravimetric measurements using a mass balance model, the activation energy of AROK was found to be 84 kJ/mole, whereas ARTOK was found to be 106 kJ/mole. The results suggest that diffusion controls the reaction of AROK, while oxidation controls the reaction of torrefied biomass. The pyrolysis of date palm stones was also studied in the TGFBR, and the kinetic expression was determined using a model fitting method. The most probable reaction mechanism for the thermal decomposition of palm stones was three-dimensional diffusion. The activation energy for experiments between 350°C and 600°C for date palm stones was 27.67 kJ/mole. Furthermore, the gasification of date palm stones was investigated at ER (0.15-0.35) and a temperature range of 600-750°C in 50°C increments. Based on the energy yield (7 MJ/kg), the results suggest that the optimum conditions were at T=750°C and ER=0.2. Overall, the result reveals that the TGFBR, in comparison with TGA, would be a viable reactor that enables kinetic analysis of gas-solid reactions under isothermal conditions, benefiting from its features. The parameters obtained from the kinetic study of TGFBR are essential in the scale-up design of useful conversion technologies such as gasification. Also, the pre-treatment of biomass via torrefaction is a promising route to improve gas production in a bubbling fluidised bed gasifier.
40
Nsamba, Hussein Kisiki. "Performance evaluation and modelling of a small-scale biomass gasifier". Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/50699/.
Testo completoAbstract (sommario):
Many parts of the World have remained underdeveloped due to the lack of access to electricity. Developing and promoting alternative energy sources from renewable materials would assist to mitigate the energy crisis in many parts especially in the World. This research examined the possibility of using a 10KW power pallet as a sustainable energy generation system especially for energy poor areas. This was achieved through the gasification of woodchips at varying moisture content, varying gasification times and at varying electrical loads while investigating the numerous changes in the major factors affecting gasification such as temperature, fuel consumption rate, equivalence ratio (ER), quality of the producer gas, heating value, carbon conversion efficiency as well as the cold gasification efficiency of the gasifier. Experimental data was analysed and interpreted by one way Analysis of Variance (Anova) to establish a relationship on the effect of the major factors affecting gasification as investigated in this study. It was discovered that the gasifier is an autothermal system that maintains a steady state of thermodynamic equilibrium for longer hours as long as the gasifier is constantly supplied with a drier fuel. The gasifier stably and optimally operates with woodchips of moisture content less than 10% to produce an energy rich gas for gasification times longer than six hours to yield a gas rich in Hydrogen (H2), Carbon monoxide (CO) and methane (CH4) at a respective concentration of up to 18.1%, 25.3% and 2.2% with a corresponding Higher Heating Value (HHV), Cold Gas Efficiency (CGE) and gas production rate of 6.4MJ/m3, 75.8% and 2.34m3/kg respectively. The reactor takes longer time to attain thermodynamic equilibrium once operated with woodchips of moisture content above 15%. This subsequently affects the quality of producer gas yielding a gas of low calorific value that would even clog the engine. The moisture content of the wood chips was found to play a very significant role in determining the values of temperatures attained and subsequently determining the quality of producer gas. The gasifier was found to produce the required energy up to the design capacity of 10KW required for several industrial applications. Increasing the engine throttle valve increased the frequency of the engine and subsequently the voltage. The designed energy output of up to 10KW could only be produced if the engine frequency was 60HZ and could be lower if the engine operated at a lower frequency. A thermodynamic equilibrium model was further developed to predict the composition of producer gas going to the engine. The thermodynamic equilibrium model yielded a gas composition of 25.99%, 23.92%, and 0.42% for CO, H2 and CH4 respectively that was in good agreement with the experimental results at 850 ºC and ER of 0.27. Similarly, the modelled gasification temperature of 870.85ºC corresponds with a minor deviation of 2.5% with the experimental gasification temperature of 850ºC. The exhaust stream composition contained Carbondioxide (CO2) of upto 20% which is on the higher side because air was used as the gasifying agent and the gasifier was completely autothermal. Such CO2 concentration ought to be lowered if the gasifier is to be adopted as a sustainable renewable energy system. The gasifier was found to operate better with wood chips in the size range between 1.3cm - 4.0cm as very fine wood chips would block the flow of air hence compromising on the sustainability of the exothermic reactions and bigger wood chip particles would not be easily broken down by the auger hence resisting the flow of the woodchips into the reactor. Operating the gasifier at optimal conditions yields a gas of high calorific value good enough to make it a reliable standalone system that could be integrated into sustainable bioenergy systems.
41
Fang, Liane Jessica, e Caroline M. Hane-Weijman. "Characteristics of pine needle combustion in a semi-gasifier burner". Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/68836.
Testo completoAbstract (sommario):
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, June 2011."June 2011." Cataloged from PDF version of thesis.
Includes bibliographical references (p. 29).
The motivation behind this report was to develop a stronger understanding of pine needle combustion behavior in a semi-gasifier, in order to ultimately design an effective pine needle cook stove for people in the developing world. Pine needles are a cheap, energy-dense fuel source that can be harnessed for cooking purposes, but they are often physically or chemically altered prior to being used as a fuel. The challenge remains to develop a stove that uses unprocessed pine needles. Using principles of a semi-gasification biomass stove, this paper explores the combustion and burn characteristics of unprocessed pine needles by measuring the effects of temperature in a configured burner when altering primary and secondary airflow into the burner. Experiments showed that pine needles in a semi-gasifier combust in two regimes--one characterized by secondary combustion of volatiles released from the primary burn of raw pine needles, and another characterized by the smoldering of pine needle charcoal. Each regime needed unique balances between primary air and secondary airflow. The first regime required a relatively low primary airflow with a high secondary airflow, while the second regime needed a high primary airflow to maintain charring and low or no secondary airflow. The balance of airflow in the first regime was crucial in determining whether the volatiles combusted or were released as plumes of smoke. The findings of this report can be used as an initial benchmark and resource in the further development of an existing proof-of-concept prototype, which was built by the authors with a team of MIT students and affiliates and a community partner in Uttarakhand, India.
by Liane Jessica Fang and Caroline M. Hane-Weijman.
S.B.
42
Mazumder, AKM Monayem Hossain. "Development of a Simulation Model for Fluidized Bed Mild Gasifier". ScholarWorks@UNO, 2010. http://scholarworks.uno.edu/td/101.
Testo completoAbstract (sommario):
A mild gasification method has been developed to provide an innovative clean coal technology. The objective of this study is to developed a numerical model to investigate the thermal-flow and gasification process inside a specially designed fluidized-bed mild gasifier using the commercial CFD solver ANSYS/FLUENT. Eulerain-Eulerian method is employed to calculate both the primary phase (air) and secondary phase (coal particles). The Navier-Stokes equations and seven species transport equations are solved with three heterogeneous (gas-solid), two homogeneous (gas-gas) global gasification reactions. Development of the model starts from simulating single-phase turbulent flow and heat transfer to understand the thermal-flow behavior followed by five global gasification reactions, progressively with adding one equation at a time. Finally, the particles are introduced with heterogeneous reactions. The simulation model has been successfully developed. The results are reasonable but require future experimental data for verification.
43
Silaen, Armin. "Simulation of Coal Gasification Process Inside a Two-Stage Gasifier". ScholarWorks@UNO, 2004. http://scholarworks.uno.edu/td/198.
Testo completoAbstract (sommario):
Gasification is a very efficient method of producing clean synthetic gas (syngas) which can be used as fuel for electric generation or chemical building block for petrochemical industries. This study performs detailed simulations of coal gasification process inside a generic two-stage entrained-flow gasifier to produce syngas carbon monoxide and hydrogen. The simulations are conducted using the commercial Computational Fluid Dynamics (CFD) solver FLUENT. The 3-D Navier-Stokes equations and seven species transport equations are solved with eddy-breakup combustion model. Simulations are conducted to investigate the effects of coal mixture (slurry or dry), oxidant (oxygen-blown or air-blown), wall cooling, coal distribution between the two stages, and the feedstock injection angles on the performance of the gasifier in producing CO and H2. The result indicates that coal-slurry feed is preferred over coal-powder feed to produce hydrogen. On the other hand, coal-powder feed is preferred over coal-slurry feed to produce carbon monoxide. The air-blown operation yields poor fuel conversion efficiency and lowest syngas heating value. The two-stage design gives the flexibility to adjust parameters to achieve desired performance. The horizontal injection design gives better performance compared to upward and downward injection designs.
44
Evans, G. D. "Development and operation of an open-core downdraft gasifier system". Thesis, Aston University, 1992. http://publications.aston.ac.uk/9784/.
Testo completo
45
Hu, Ming. "Instrumentation and tar measurement systems for a downdraft biomass gasifier". Thesis, Manhattan, Kan. : Kansas State University, 2009. http://hdl.handle.net/2097/1678.
Testo completo
46
Gunarathne, Duleeka. "Optimization of the performance ofdown-draft biomass gasifier installedat National Engineering Research &Development (NERD) Centre ofSri Lanka". Thesis, KTH, Kraft- och värmeteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-78994.
Testo completoAbstract (sommario):
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.
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Brown, Jock William. "Biomass Gasification: Fast Internal Circulating Fluidised Bed Gasifier Characterisation and Comparison". Thesis, University of Canterbury. Chemical and Process Engineering, 2006. http://hdl.handle.net/10092/1187.
Testo completoAbstract (sommario):
In 2004 the Department of Chemical and Process Engineering (CAPE) at University of Canterbury began a programme to investigate using biomass gasification integrated combined cycle (BIGCC) technology to convert waste products and residues to useful energy for the wood processing sector. This research was conducted as a part of Objective Two of the programme to develop gasification and gas cleaning technology. This project involved commissioning and characterising the operation of the Fast Internal Circulating Fluidised Bed (FICFB) gasifier and comparing its operation with a more conventional up-draught process owned and operated by Page Macrae in Mount Manganui. The wood derived gas composition of each gasifier was measured using gas chromatography and these compositions were used to calculate lower heating values (LHV). The CAPE FICFB gasifier has proven to produce successfully a gas with a lower heating value of 10400-12500 kJ/Nm³. The Page Macrae gasification process produces a low quality gas with a lower heating value of 4100-5100 kJ/Nm³. This is much lower than the CAPE gasifier since the oxidant used in the up-draught gasification process is air and the product gas is diluted by nitrogen. The Page Macrae gasification system combusts wood derived gas to produce steam for a laminar veneer lumber (LVL) processing plant so gas quality and heating value are less important than in electrical production applications. Reducing the nitrogen content of the CAPE product gas will increase the heating value of the gas. Improvements to the boiler system will reduce the amount of air required for gasification and hence reduce the nitrogen content. Further improvements to gas quality can be gained from a change in the fuel feed point from on top of the gasification column's bubbling fluidised bed to the side of the bubbling fluidised bed. The CAPE gasifier is much more complicated and requires specialised operators but produces a gas suitable for gas engine and gas turbine technology. Overall the CAPE gasification system is more suited to BIGCC applications than the Page Macrae process.
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Gopalakrishnan, Prasanth. "Modelling of Biomass Steam Gasification in a Bubbling Fluidized Bed Gasifier". Thesis, University of Canterbury. Chemical and Process Engineering, 2013. http://hdl.handle.net/10092/8675.
Testo completoAbstract (sommario):
This thesis presents the numerical simulation study of the biomass-steam gasification in a bubbling fluidized bed (BFB) gasifier including the mathematical model development and the experimental validation of the model developed. The study focused on two main areas on developing the mathematical model: a one-dimensional (1D) non-isothermal reaction kinetics model and a two-dimensional (2D) model consisting of the reaction kinetics model for gasification reactions and two-dimensional CFD model for hydrodynamics characteristics.
The biomass gasification with steam as the gasification agent at elevated temperatures can be considered to include two main stages: initial pyrolysis and subsequent gasification reactions. In the first stage, the pyrolysis reactions of the biomass occurred instantaneously for a short duration decomposed into volatile gases, char and tar at the bottom of the gasifier filled with the bed materials. In the subsequent stage of gasification, reactions occurred among the gasification agent (steam), the volatile gases and the char evolved from the initial stage of pyrolysis at high temperatures. The producer gas from biomass-steam gasification mainly consists of CO, H2, CO2, CH4 and H2O and least quantities of higher hydrocarbons at elevated operating temperature. Hence the reactions such as Steam Gasification reaction, Water Gas-Shift reaction, Methanation reaction, Bouduard reaction, and Steam Methane Reforming reaction were considered. The final gas composition of the producer gas was affected by the products of pyrolysis process which were quantified with a product distribution function of temperature developed from experimental results in this work.
The development of the subsequent gasification reaction model was based on two-phase theory of gases and solids consisting of the particle-lean bubble phase and the particle-rich emulsion phase which were distributed homogeneously when the gas velocity through the bed was in excess of the minimum fluidization velocity. In the two-phase theory model, the heat and mass transfer rates were related to the fluidization characteristics of the bed. Therefore, understanding and quantitatively description of the hydrodynamics of the gas-solid within the gasifier were important which were adopted from literature for the development of the 1D model for the gasification process in the BFB.
In the 1D gasification model, the non-linear partial differential equations (PDEs) describing the mass and energy balances (for both phases) with the reactions kinetics based on Arrhenius correlations were numerically solved using a solver function from the PDE modules of Matlab software with properly defined initial and boundary conditions. In the development of the 2D gasification model, the developed reaction kinetics model was integrated into the 2D CFD Eulerian-Eulerian granular kinetic model called Gasification embedded 2D CFD model using CFD ANSYS FLUENT 12.1 package. In this 2D model, the built-in ‘laminar finite-rate’ model was adopted to describe the chemical kinetics using Arrhenius reaction kinetics expressions. The momentum equation considered laminar viscous model for laminar flow at low steam to biomass (S/B) ratio (lower than 0.6) and k-ε turbulence viscous model for transient to turbulent flow regime for high S/B ratio. These were solved using a Phase Coupled SIMPLE solver algorithm based on FVM.
To provide validation data for the developed biomass gasification models, experiments were undertaken on the 100kW DFB gasifier at the University of Canterbury. In the experiments, it had been found that the simulation results from the initial pyrolysis model were in close agreement with the experimental data with discrepancies of ±1.0% (mol/mol) for H2, ±0.8% (mol/mol) for CO, ±0.6% (mol/mol) for CO2 and ±0.3% (mol/mol) for CH4.
After this, the gasification agent steam was introduced for normal gasification operation under various operation conditions (temperature, S/B ratio). The experimentally measured producer gas compositions for the operating conditions of 680-780oC, 1 atmospheric pressure and S/B ratio of 0.53 ranged from 17.9% to 28.3% for H2, from 35.7% to 38.5% for CO, from 23% to 28.8% for CO2 and from 13% to 15% for CH4 (mol/mol on dry basis). Under the above operation conditions, the discrepancies between the experimentally measured producer gas compositions and the predicted results using the 1D model were, respectively, 4.5% for H2, 1.4% for CO, 7.5% for CO2 and 1.2% for CH4 (mol/mol on dry basis). For the 2D model, the discrepancies were, respectively, 2.4% for H2, 2.9% for CO, 4.9% for CO2 and 0.8% for CH4 (mol/mol on dry basis). However under the operating conditions of 780oC and S/B ratio of 0.53, the predicted CO2 and H2 concentrations from the 2D model were, respectively, 8.6% (mol/mol on dry basis) higher and 4.8% (mol/mol on dry basis) lower than the measured value.
The experimentally measured producer gas compositions for the operating conditions of 710oC and S/B ratio of 0.33-0.84 ranged from 24.4% to 32% for H2, from 32.7% to 44.2% for CO, from 15% to 21.8% for CO2 and from 13.6% to 16.4% for CH4 (mol/mol on dry basis). The discrepancies between experimentally measured producer gas compositions and the model predicted results for the above operating conditions were 1.6% for H2, 2.7% for CO, 1.8% for CO2 and 0.6% for CH4 (mol/mol on dry basis) for the 1D model while those for the 2D model were 4% for H2, 1.6% for CO, 1% for CO2 and 1.6% for CH4 (mol/mol on dry basis).
From the model validation, it was found that the 1D model results and 2D model simulation results were closely in agreement and show small discrepancy with the experimental results. In addition, the 1D model uses less computing time than the 2D model; therefore, the 1D model has been used to investigate the effects of operating conditions (temperature and S/B ratio) on the producer gas composition. It was observed that the gas concentration of CO, CO2 and CH4 in the producer gas decreased while the H2 increased with increasing operating temperature in the examined range from 680-780oC. Similarly the gas concentration of H2 and CO2 in the producer gas increased while CO and CH4 decreased with increasing S/B ratio in the examined range from 0.33-0.84.
The 2D model can be used to predict gas distribution within the gasifier thus it can be used to gain better understanding of the gasification process and effect of gasifier configuration and operating conditions on the gasifier performance. Further studies are proposed for improvements on the 2D model.
49
Ranwell, Pierre. "A numerical model of the moving bed gasifier / by Pierre Ranwell". Thesis, North-West University, 1997. http://hdl.handle.net/10394/3660.
Testo completoAbstract (sommario):
The moving bed coal gasifier produces 89 percent of the world's gas from coal. In South Africa the largest sector of the chemical and petrochemical industries is dependant on products from these gasifiers. Little is known about the transfer processes in the gasifier because it is not possible to get accurate information on the transfer process by means of experimentation.
In this study the transfer processes in the gasifier were simulated by computational fluid mechanics. Firstly a one-dimensional numerical model was developed to simulate the mass and energy transfer of the height dimension of the gasifier. The model consists of reaction rates of seven reactions that occur in the gasification process. The results obtained compare well with those of similar published models as well as with observations on gasifiers in operation.
Secondly, a three-dimensional chemical reacting flow model that incorporated the mass and momentum transfer of the fluid in a moving packed bed, was developed. The model was compared with the one-dimensional model, as well as with results achieved from gasifier excavations. These comparisons proved that the three-dimensional model was a more reliable simulation of the gasification process. Finally, the model was applied to study some of the transfer mechanisms in the gasifier. It became clear from the simulation that the fundamental cause of temperature instabilities in the gasifier was the non-homogeneous spread of coal particle size inside the gasifier. It was finally demonstrated that the model developed could be applied to a wide range of studies on gasification.Thesis (Ph.D. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 1998.
50
Rabell, Ferran Santiago. "Modeling and exergoeconomic analysis of biomass gasification in a downdraft gasifier". Thesis, KTH, Skolan för kemivetenskap (CHE), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-146595.
Testo completoAbstract (sommario):
In this work it is presented an equilibrium model, capable to predict the composition of the generated gas, its Lower Heating Value (LHV), the gasification efficiency, the ratio air/biomass and the ratio gas/biomass in a downdraft gasifier. The model describes the influence of the moisture content of the biomass and the gasification temperatures on the composition and properties of the produced gases, like the low heating value (LHV). It is assumed that all the chemical reactions taking place in the gasification area are in thermodynamic equilibrium. The model doesn't considered tar formation. It is not considered formation of other hydrocarbons (CxHy) than methane. The types of biomass used for modelling are: sugarcane bagasse, paddy husk, pine sawdust, mixed paper waste and municipal solid waste. The effect of gasification temperature and moisture content of biomass over the gas composition has been also investigated. Also an exergo-economic analysis of cogeneration system forming by a downdraft gasifier associated to an internal combustion engine was carried out, using sugar cane bagasse, rice husk, and pine sawdust, as fuel in gasification processes. At 700°C the highest amount of CO and CH4 are produce. The amount of CH4 and CO decrease with the temperature when the gasification temperature is increased from 700°C to 1000°C. The amount produced H2 does change so much between the gasification at 700°C and 1000°C. But the amount produced hydrogen is somewhat higher at 800°C. The lower heating value (LHV) of the synthesis gas from gasification of sugarcane bagasse the LHV of the produced gas is 4,09MJ/Nm3; for gasification of pine the LHV of the produced gas is 5,32MJ/Nm3; for gasification of rice husk the LHV of the produced gas is 3,14MJ/Nm3, for gasification of mixed paper waste the LHV of the produced gas is 4,51%, and for gasification of municipal solid waste the LHV of the produced gas is 3,95MJ/Nm3. The cold and hot efficiency of gasification process at 800°C for bagasse with 20% moisture content are 55,32% and 84,90% respectively.