Graduation date: 1998

Experiments were conducted in a 0.91 m diameter half-cylindrical spouted bed/spout-fiuid bed column equipped with a 60° conical base and semi-circular inlet orifice diameters of 76 to 140 mm. Three particulate solid materials were studied: 3.25 mm polystyrene, 4.72 mm brown beans and 6.71 mm green peas. Beds with static depths of 0.55 to 2.60 m were contacted with air, both in the standard spouted bed and the spout-fluid bed mode. The dependent hydrodynamic parameters studied included minimum spouting velocity, maximum spoutable bed height, spout shape and diameter, fountain height, dead zone dimensions, overall bed pressure drop, fluid distribution in the annulus, longitudinal and radial pressure profiles in the annulus, and regime maps for the spout-fluid bed. Correlations for minimum spouting velocity developed on smaller vessels generally gave poor predictions for the large diameter vessel employed in this work and failed to predict the observed dependence of U[formula omitted]₈ on the static bed height. The empirical correlation due to McNab (1972) was found to predict the average spout diameter very well for standard spouted beds, while the correlation due to Hadzisdmajlovic et al. (1983) gave a reasonable prediction for spout-fluid beds. Substantial dead zone regions where particles were stagnant were observed in the lower portion of the vessel. The Littman et al. (1977) equation overestimated the maximum spoutable bed height, while the McNab and Bridgwater (1977) equation gave a value which appeared to be far too high. The observed fountains were extremely dilute, and their heights always exceeded the corresponding static bed heights for the conditions studied. The Epstein and Levine (1978) equation gave good estimates of overall bed pressure drop. The longitudinal fluid velocity in the annulus was well predicted by the modified Lefroy-Davidson (1969) equation due to Epstein et al. (1978) and was reasonably predicted by the Mamuro-Hattori (1968) model in the cylindrical portion. However, both equations gave poor predictions in the conical base portion. In the conical base section, the Rovero et al. (1983) equation predicted the correct trend, but consistently overestimated U[formula omitted] by a considerable margin. Both the Epstein and Levine (1978) equation and the Lefroy and Davidson (1969) equation were found to be in good agreement with the experimental longitudinal pressure profiles. The radial distribution of pressure in the annulus for any bed level was observed to be nearly constant when there was auxiliary flow. A computer model based on the Ergun equation gave useful qualitative predictions of the fluid flow distribution in the annulus. Four fairly distinct flow regimes were delineated in this work for cases where there were auxiliary air flow: (1) spouting-with-aeration; (2) spout-fluidization; (3) submerged jets, slugs and bubbles in fluidized bed, and (4) packed bed. The minimum total fluid flowrate for spouting-with-aeration always exceeded the minimum spouting flowrate, but was smaller than the minimum fluidization flowrate. The minimum total fluid flowrate for spout-fluidization was found to be equal to the minimum fluidization flowrate. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Many industrial processes require contact between particles and a fluid or spray in order to effect drying, coating or granulation. One device capable of contacting fluid and particles efficiently is a spouted bed in which a jet of fluid is injected into solid particles. This forms an open channel or spout and induces material circulation in a downward moving annulus. For the continuous throughput of solids, knowledge is required of the mixing and particle motions within the bed. When processing mixtures of particles differing in size or density, the components are often found to segregate into regions rich in larger or denser particles. In a spouted bed this tendency could affect the mixing of solids and residence times of different size fractions with which the process performance is associated. Distributions of particle residence times were measured using a novel magnetic method of tagging. A thin coat of soft iron powder was applied to form tracer particles, a technique having potential for the investigation of mixing in many industrial processes. In this study, perfect mixing was observed for mono-size particle feeds and perfect self-mixing of each component in binary-size feeds. Generally, although not universally, the smaller particles in a mixture passed through the bed more quickly than larger particles. As the bed depth and gas flow rate were increased independently, the difference between the mean res- idence times of the components became greater and was also shown to be dependent on the position of the solids outlet. The difference in residence times is attributed to segregation within the bed. Different residence times for each component will arise if the particles segregate in the spout, the fountain, the free surface, the annulus or as they are drawn off from the outlet. From the studies on a 150 mm diameter bed, the key processes occur on the free surface and in the neighbourhood of the outlet. In larger diameter beds, segregation on the free surface is predicted to be of prime importance, especially when economy dictates the operation of the bed at low gas flow rates. The particles would then be deposited on the free surface near the spout and the cascading of solids towards the perimeter would lead to segregation.

No description available.

Combustion of Minto coal, a sub-bituminous eastern coal which is highly agglomerating and has a high sulphur content, was carried out in a 0.15 m internal diameter half-column spout-fluid bed combustor in inert beds of sand, with limestone addition for sulphur capture. The average bed temperature ranged from 800 to 900°C, flue gas oxygen level was 2.5 to 11.0%, auxiliary to total air was 0 to 0.50, and Ca/S molar ratio was 2.5. High vale coal was employed in hydrodynamic runs. Aspects studied included combustion efficiency, sulphur capture efficiency, axial and radial temperature profiles, axial O₂ and CO₂ concentration profiles, axial SO₂ concentration profiles, minimum spouting velocity, spouting stability, and maximum spoutable bed height. The principal problem encountered with Minto coal in this equipment was agglomeration during the heat-up period. A spout-fluid bed has proved to be great favourable for handling agglomerating coal relative to the standard spouted bed. When limestone was used as bed material, less sintering was encountered. However, limestone could not stand up to spouting for prolonged periods because of excessive attrition. Combustion efficiencies were found to be higher than 80% in the temperature range of 800 to 900°C without solid fines recycle. An increase of temperature between 800°C and 840°C was beneficial for combustion efficiency, while a further increase up to 885°C did not seem to have a significant effect on combustion efficiency. Increase of auxiliary/total air ratio was favourable to combustion efficiency at elevated temperatures. Sulphur capture efficiency passed through a maximum with increasing temperature between 800°C and 900°C The maximum value was obtained at around 830°C. NOx emission increased linearly with increasing flue gas oxygen level. No abrupt temperature increase above the bed surface was observed in both spouted and spout-fluid beds investigated in the present study. Temperature may increase above the bed surface for low excess oxygen runs in view of the substantial amount of combustion found to occur in the freeboard. Temperatures were more uniform after the introduction of auxiliary air. Most oxygen was consumed below the bed surface. Axial profiles showed a significant SO₂ jump in the spout over the bed height. Combustion and sulphation could be considered to occur in two main stages: (1) Combustion of carbon, at the same time as most of the sulphur is released. (2) Sulphation of the sorbent. The Mathur and Gishler (1955) and Wu et al. (1987) equations gave poor agreement with the minimum spouting velocity, Ums, over the entire range of temperature. For large particles Ums tended to increase with increasing temperature, while for small particles it decreased with increasing temperature. Gas viscosity should be taken into consideration for predicting Ums. A considerably greater effect of auxiliary to total air ratio, q/Qt, on total minimum spouting velocity was found at elevated temperatures than at room temperature. At the maximum spoutable bed height, the value of Um/Umf was found to decrease with increasing temperature and to be smaller than unity at elevated temperatures. The McNab and Bridgwater (1977) expression correctly predicted the observed trends of Hm and worked reasonably well at high temperatures, although it was found to over-predict Hm at lower temperatures. Hm decreased with increasing temperature for all particle sizes, with a faster decrease for smaller particles. Fluidization in the annulus was never observed as the termination mechanism of spouting at high temperatures. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

No description available.

The central aim of this thesis is to support the efforts to counteract certain environmental problems caused by emissions of volatile organic compounds. The purpose of this work was (1) to develop a method to establish the amount of emitted substances from dryers, (2) to determine the effect of drying medium temperature and end moisture content of the processed material on emissions of monoterpenes and other hydrocarbons, (3) to examine the emissions of monoterpenes during production of pellets, and (4) to examine the natural emissions from forests with an eye to implications for modelling. The measurement method (1) resolves the difficulties caused by diffuse emissions, and also solves the problems associated with high moisture content of the drying medium. The basic idea is to use water vapour to determine the exhaust flow, while a dry ice trap is used both to preconcentrate emitted volatile organic compounds and to determine the moisture content of the drying medium. The method as used in this paper has an uncertainty of 13% using a 95% confidence interval. Emissions from a spouted bed (2) in continuous operation drying Norway spruce sawdust at temperatures of 140°C, 170°C or 200°C was analysed with FID and GC-MS. When the sawdust end moisture content was reduced below 10%wb, emissions of terpenes and volatile organic compounds per oven dry weight increased rapidly. Increased temperature of the drying medium increased the amounts of emitted monoterpenes when sawdust moisture content was below the fibre saturation point. Examination of sawdust and wood pellets from different pellets producers (3) revealed that most of the terpene emissions happened during the drying step, with rotary dryers causing higher emissions than steam dryers. Almost all of the volatile terpenes remaining in wood after drying were released during pelleting. When sawdust with higher moisture content was used in the pellets press, the terpene emissions were increased. Terpenes emitted naturally from vegetation can have an adverse environmental impact. Factors affecting terpene emissions from tree species in Sweden were reviewed (4). Models for prediction of terpene fluxes should include not only temperature but also light intensity, seasonal variation, and a base level of herbivory and insect predation. Prediction of high concentrations of ambient terpenes demand sufficient resolution to capture emission peaks e.g. those caused by bud break.

Orientador: Sandra Cristina dos Santos Rocha / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-15T13:40:56Z (GMT). No. of bitstreams: 1 Rosa_GabrielaSilveirada_M.pdf: 1952306 bytes, checksum: 6e39c34ab96794dd18a4ddc2c6083579 (MD5) Previous issue date: 2010 / Resumo: A uréia é o fertilizante nitrogenado mais utilizado no Brasil, e seu uso tem aumentado nas últimas décadas. O recobrimento das partículas de uréia é realizado, principalmente, para que o nitrogênio tenha uma liberação lenta, aumentando assim seu tempo de disponibilidade para as plantas. O objetivo deste trabalho foi recobrir os grânulos de uréia com uma suspensão aquosa de natureza polimérica em leito de jorro, a fim de minimizar as perdas de nitrogênio (amônia) por volatilização. O desenvolvimento do trabalho consistiu em: caracterizar as partículas de uréia; formular e caracterizar a suspensão de recobrimento; estudar a fluidodinâmica da partícula no leito de jorro; desenvolver um planejamento experimental do tipo composto central rotacional para o recobrimento; e avaliar a liberação de nitrogênio por volatilização. As variáveis estudadas no planejamento foram: temperatura do ar de jorro (Tar), vazão da suspensão de recobrimento (Ws) e pressão do ar de atomização (Pat); e como respostas avaliou-se a eficiência do recobrimento e o crescimento da partícula. Os resultados para a eficiência do processo de recobrimento e crescimento da partícula ficaram na faixa de 44 a 74 % e 1,1 a 2,6 %, respectivamente. Após a realização do planejamento experimental, fazendo uso das condições otimizadas, determinou-se a cinética de crescimento da partícula, obtendo-se um coeficiente de crescimento linear de 1,13.10-3 min-1. Nestas mesmas condições realizou-se o recobrimento utilizando vinhaça, em substituição à água, na suspensão de recobrimento, resultando em valores de eficiência e crescimento similares aos obtidos com o uso da suspensão aquosa. As análises de volatilidade mostraram que o filme de recobrimento proporcionou diminuição das perdas por volatilização na faixa de 3 a 57 %, sendo estes resultados bastante satisfatórios. As análises obtidas por microscopia eletrônica de varredura demonstraram que o filme formado sobre as partículas recobriu toda superfície de forma uniforme e homogênea / Abstract: Urea is the most used nitrogen fertilizer in Brazil, and its use has been increasing in the last decades. The coating of urea particles is accomplished, mainly, to obtain slow liberation of the nitrogen content, increasing its availability for the plants. The aim of this work was to analyze the urea particles coating with an aqueous polymeric suspension in spouted bed, in order to minimize nitrogen (ammonia) losses by volatilization. The development of the work consisted in: physically characterizing the urea particles; formulating and characterizing the coating suspension; studying the fluid-dynamic of the particles in the spouted bed; developing a central composite rotatable design (CCRD) of experiments for the coating process; and evaluating the nitrogen release by volatilization. The effects of inlet air temperature, coating suspension flow rate and atomizing air pressure on the coating process efficiency and on particle growth were analyzed. The results showed efficiency and particle growth in the range of 44 to 74 % and 1.1 to 2.6 %, respectively. The urea growth kinetics during coating was determined for the optimal operating conditions and a linear growth coefficient of 1.13.10-3 min-1 was obtained. At these same optimal conditions, the coating was carried out using vinasse in the formulation of the suspension, in substitution to the water. Similar results for efficiency and particle growth were obtained compared to the ones using the aqueous suspension. The volatilization analyses showed that the polymer film coating provided a decrease of the nitrogen loss in the range of 3 to 57 %, being these results well satisfactory. The quality of the coated surface was analyzed by scanning electronic microscopy (SEM) and showed uniform and homogeneous distribution of coating layer / Mestrado / Engenharia de Processos / Mestre em Engenharia Química

Orientadores: Florencia Cecilia Menegalli, Rosiane Lopes da Cunha / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-14T14:28:38Z (GMT). No. of bitstreams: 1 CiroVelasquez_HectorJose_D.pdf: 3600504 bytes, checksum: efd0571f00b5ea398f5836590f0165bb (MD5) Previous issue date: 2009 / Resumo: Suspensões de gomas xantana e de l-carragena foram secas usando um secador de leito de jorro fluidizado com partículas inertes de vidro e plásticas de ABS (acrylonitrile butadine styrene). O processo de secagem foi avaliado quanto ao desempenho do secador (eficiência de produção de pó e retenção de sólidos), características fluidodinâmicas (velocidades da partícula inerte no jorro e ânulo, queda de pressão no leito, largura da fonte, altura máxima de jorro, distribuição de temperaturas no leito) e qualidade do produto final obtido (propriedades reológicas e teor de umidade). Um planejamento fatorial 23 com 2 pontos centrais e 6 pontos axiais e superfícies de resposta foi usado para determinar o efeito das condições de secagem (temperatura de ar, vazão de suspensão e vazão de ar no jorro e ânulo) sobre o processo e na qualidade do produto final. Os resultados mostraram que foi possível obter produto reconstituído de pó de xantana usando vidro ou ABS como inerte. No entanto, para suspensões de l- carragena não foi possível a secagem com partículas esféricas de vidro devido à alta tensão superficial e baixo ângulo de contato. De acordo com os resultados do planejamento experimental, a eficiência de produção média de pó de goma xantana usando vidro como inerte foi de 28% com uma retenção de sólidos de 65%, enquanto que usando ABS a produção média foi de 45% e a retenção de sólidos de 49%, ou seja, o melhor desempenho do secador ocorreu quando ABS foi empregado como partícula inerte. Para a secagem de suspensões de l-carragena com partículas de ABS a eficiência de produção média de pó foi de 23% e a retenção media foi de 71%. A variável mais relevante na secagem das suspensões de gomas xantana e carragena foi a vazão de suspensão, sendo que um aumento desta variável produziu um baixo rendimento de pó e aumentou a retenção de sólidos dentro do leito. A queda de pressão do leito apresentou uma variação periódica indicando uma instabilidade fluidodinâmica. A distribuição de temperatura no leito mostrou uma operação quase isotérmica e que o processo evaporativo ocorreu principalmente na zona do jorro e base do ânulo. A velocidade da partícula no jorro foi dependente da vazão de ar na região do jorro, enquanto que a velocidade da partícula dentro no ânulo foi função da vazão de suspensão e também da vazão de ar que passava pelo jorro. A xantana obtida pela secagem em jorro fluidizado formou suspensões de natureza altamente pseudoplástica e com propriedades viscoelásticas de gel fraco. A vazão de alimentação da suspensão (=1 g/min) foi um fator importante para a preservação da qualidade reológica. A secagem de suspensões de goma xantana realizada em condições ótimas, tanto em leitos com partículas de ABS quanto de vidro, não mostrou efeito na qualidade reológica do produto. O produto reconstituído de l-carragena obtido nas condições otimizadas de secagem também formou suspensões de natureza altamente pseudoplástica, porém com propriedades viscoelásticas características de suspensões altamente diluídas (G''>G'), mostrando valores de viscosidade, módulos elástico (G') e de perda (G'') menores que o produto comercial e portanto uma perda de qualidade do produto. Nas condições de melhor desempenho do secador, as suspensões de l-carragena foram mais susceptíveis a sofrer mudanças em sua estrutura molecular que a goma xantana / Abstract: Xanthan and l-carrageenan suspensions were dried using a two dimensional spouted fluidized bed dryer with inert particles of glass and ABS (acrylonitrile butadine styrene).The dryer performance (powder production and solid retention), fluid flow characteristics (particle velocity in the spout and annulus, pressure drop, fountain width, maximum spout height, distribution of temperatures inside the bed) and quality properties of final product (rheological properties and moisture content) were evaluated. A complete 23 factorial design with 2 central points and 6 axial points together with response surfaces analysis was used to determine the effect of the drying conditions (drying temperature, suspension mass flow and air flow in the spout and annulus) on the drying process and final product. The results showed that it is possible obtain a reconstituted powder of xanthan gum using glass and ABS as inert particles. However, for suspensions of l- carrageenan was not possible the drying with glass spherical particles due to high superficial tension (low angle of contact). According to results of experimental design the mean powder production of xanthan gum using glass as inert was of 28% with a solid retention of 65%, whereas using ABS the mean powder production was of 45% with a solid retention of 49%, thus the best performance of the drier occurs when the bed with ABS is operated. In addition, the drying of l carrageenan suspensions with ABS particles showed a me n production of 23% with a solids retention of 71%. The most significant variable in the drying of the suspensions of xanthan and l carragena gum was the suspension mass flow rate where an increases produces a diminishing of the powder production increasing the solids retention in the bed. The pressure drop in the bed presented a periodic variation with the processing time indicating a hydrodynamics instability. The temperature distribution in the bed showed that annulus zone operated almost isothermally and that the spout zone and the annulus base are the zones where occurs the evaporative process. The particle velocity in the spout depends upon of the air flow in the spout, whereas the particle velocity in the annulus is function of the aeration and suspension mass flow rate. The reconstituted xanthan powder produced suspensions of highly pseudoplastic nature and with viscoelastic weak gel properties. The suspension mass flow rate (=1 g/min) was a factor important to preserve its rheological quality. To xanthan gum the drying operating conditions evaluated in the optimum point showed that the inert particle (ABS and glass) not influenced on the rheological quality of the reconstituted product. The l-carrageenan suspensions evaluated in the drying optimum conditions formed suspensions of highly pseudoplastic nature with viscoelastic properties of suspensions highly diluted (G''>G'). Also, the rheological and viscoelastic characteristics as viscosity, storage (G') and loss moduli (G'') are lower than commercial gum indicating a severe loss of product quality. In the conditions of better performance of the dryer, the suspensions of l- carrageenan were more sensitive to suffer changes in its molecular structure than the xanthan gum / Doutorado / Doutor em Engenharia de Alimentos

Hydrodynamics and heat transfer characteristics found in fluidization were studied in a small scale laboratory fluidized bed. Experiments were designed to capture field data on multiple slit jet gas distributor systems for the validation of computational models. Localized data was quantified through the use of several novel non-intrusive experimental measurement techniques. The analyses provide a unique study that connects full field-of-view multiphase flow dynamics with transient heat transfer distributions. The gas-solid hydrodynamics were captured through three non-invasive measurement techniques, viz. Particle Image Velocimetry (PIV), Digital Image Analysis (DIA), and pressure drop spectral analysis. The effects of inlet gas flowrate, Geldart B and D classified particle types, and the number inlet gas slit jets were investigated. Frequency analysis of a differential pressure signal resulted in the classification of four difference flow regimes. The coupling of PIV with DIA captured particle velocity, solid circulation rates, average cycle times, dead zone sizes, jet merging effects, gas void fraction distributions, and maximum expanded bed heights. The heat transfer in fluidized and spouted beds containing a heated inlet gas source was studied through transient heat transfer measurements and analyses. Innovative experimental procedures were introduced to quantify bed-to-wall and gas-to-particle heat transfer characteristics. Two techniques were developed to overcome the spatial, time varying, and instrumental intrusive limitations often found in multiphase flow heat transfer studies. Infrared thermography was utilized along with derived discrete differential equations, and an inverse heat conduction analysis to solve for transient localized heat flux profiles and heat transfer coefficient distributions. As a result new data containing increased spatial resolution is presented on gas, wall, and particle temporal maps. Computations based from the thermal gradients quantified bed-to-wall heat flux profiles, gas-to-particle heat transfer coefficients, and localized rates of energy stored. / Master of Science